I've played the deck a lot so why not.

Monoblue is an aggro-control deck. You get on the board early, land a big threat, and then protect the threat with counters. It is a capable deck, recently finishing #2 at GP Lille, and if you ever get ahead on the board it often feels like you can't lose. However, it is somewhat inconsistent (you need to draw creature, Curious Obsession, and protection), and you're unable to kill your opponent's creatures, which means you can outright lose to e.g. T1 Llanowar Elves on the draw, Lyra Dawnbringer, or Goblin Electromancer. The deck is awful at playing from behind; you generally have to hope to draw Tempest Djinn and the opponent can't remove it. It's not an easy deck to play: it's very important to know when to hold up mana. Finally, the dice roll matters a lot, and your win percentage shoots up if you're on the play.

I suspect the deck won't be very popular among pro players for some of these reasons, and feeling like you've lost the match when you lose the dice roll is very miserable. Nonetheless, it is a capable deck, it has good matchups against some of the top decks in the meta, and it's really cheap to build. If you play on Magic Arena I can recommend it not just because of how cheap it is, but also because the matchmaking algorithm seemingly doesn't realize that you're a competitive deck and pairs you against people on preconstructed decks. Sadistic, but whatever gets the dailies done.

Card discussion
1-drops
Curious Obsession - this card is your most important card. It's the card you most want to see in your opener. It's how you draw more counters than the opponent has removal. It's so important that if it weren't for the 4-card restriction I'd guess that monoblue decks would run 8 or maybe even more copies. A couple of warnings about this card. First, it falls off if you don't attack. Second, after you've cast it, the creature you enchant is a big removal magnet. If you're holding protection, the turn you play it is an important time to hold up mana. Finally, try to play this only if you can connect the turn you play it.
Mist-Cloaked Herald - this card is also core. It's imperative to get on the board as soon as possible, and since it can't be blocked, it is the best Curious Obsession target. Run four.
Siren Stormtamer - this card is also core, since it lets you hold up protection while still pinging the opponent for one per turn. Notably, it can counter targeted abilities such as Ravenous Chupacabra's ETB effect. Run four. Note it's a wizard, which is great for Wizard's Retort.
Dive Down - a 1-mana protection effect, this is quite strong. You have a lot of these protection effects but no other one-mana ones (Siren Stormtamer is one mana to activate, but you need one mana too to get it onto the board). You don't have to run 4 however, and it depends on the meta you're predicting. I'd generally go with 2-4. A couple of notes about this card: don't neglect that it's a combat trick, and can e.g. let your Tempest Djinn win a fight against an opponent's Tempest Djinn. Also note that it can only target your creatures. That means you can't fizzle your opponent's auras etc by targeting their target.
Spell Pierce - it's a one mana counter that will counter most targeted removal early in the game. Later it's significantly weaker, but it can still get some cards that Dive Down cannot, such as The Eldest Reborn, Teferi, and so on. I would not go to the full four copies because it's inflexible and some decks don't have many non-creature spells, but 1-3 is reasonable.
Opt - the allure of this card is that it lets you hold up mana for protection and still do something proactive if the opponent doesn't do anything worth countering. It's also a 1-mana instant that helps you find Curious Obsession. I did not run it initially, but it's been growing on me. If you run Opt, run the full four copies.

2-drops
Nightveil Sprite - a 1/2 flyer with a nice effect. If you're drawing multiple cards already with Curious Obsession, the surveil helps you draw into even more protection; it also helps you draw Curious Obsession in the first place. The downside is that one point of damage a turn is not fast, and it can be stonewalled by a bigger creature in which case it's mostly useless. This competes with Warkite Marauder below. Choose one of the two and run 2-4.
Warkite Marauder - I've not actually played with this card, but it's obviously reasonable. As a 2/1 flyer it's a good clock for a 2-mana creature, and can attack into e.g. a Shalai, but it dies to Goblin Chainwhirler and doesn't improve your draws. This competes with Nightveil Sprite above. Choose one of the two and run 2-4. MTGA players only: this card is a rare. I don't know how much this improves the deck you'll play against.
Merfolk Trickster - this card is core. It lets you hold up protection and still advance your board. In addition it lets you tap key creatures as well as disable their abilities. Because you can't actually beat a strong resolved creature, sometimes your only option is to race, and Trickster is the only way you'll get enough damage past e.g. a Lyra before she takes over the game. It's also a wizard for Wizard's Retort. Run 4.
Essence Scatter - answers creatures, obviously. It's critical against cards like Steel-Leaf Champion, which is enough of a clock that you want to counter it, but spending a Wizard's Retort on it is obviously pricey. Essence Scatter improves if you're on the draw and sometimes it's your only defense against other creature decks. How many to run depends on the meta you expect, and anything from 0-4 is possible.
Chart a Course - monoblue wants to attack a lot, so the condition on this should be easy to trigger. This then becomes a 2-mana draw 2, which is strong. You can't run too many since you are not a full control deck, you still need to apply pressure, and if you're on the back foot you cannot afford to take time off to draw. Run ~2 copies.
Negate - more powerful than Spell Pierce but twice the mana cost, run this card if you expect a lot of control.
Disdainful Stroke - generally a sideboard card for decks with expensive spells.

3-drops
Tempest Djinn - this card is core. It's one of your only ways to stabilize a board if you fall behind, and it's a strong clock on its own. The downside is that it's expensive for a deck running as few lands as you do, but it's still too powerful to not run. All four copies is the standard.
Wizard's Retort - a catch-all counter. You have eight wizards in the deck (Stormtamer, Trickster) which lets you cast it for 2 mana a decent amount of the time as well. I consider this card core. Run all four copies.
Exclusion Mage - it's a strong tempo tool, but doesn't actually answer the creature unless you have 5 mana and are holding Essence Scatter. Since many of your creatures are evasive it doesn't often enable an attack either (you'd already be able to attack). You can still run up to four copies though if you predict decks with expensive creatures.

4-drops
Sleep - monoblue is very bad at playing from behind. This card is sometimes the only way you'll win a race, making it a powerful haymaker. But it's a 4-mana card, and as a tempo deck with a low land count you simply cannot afford to run too many expensive spells. Drawing multiples is also a disaster. I would not play more than 2.

Lands
I've seen anything from 18 to 22 lands, with most running 19-21 Islands. Hitting land drops is good since it lets you advance your board while still holding up protection, but flooding is an easy way to lose. How many to run depends on your curve. Sleep is the obvious one, and the more copies of Sleep you have the more lands you want also, but other cards like Exclusion Mage and even Essence Scatter (if you replace 1-mana cards) mean you should increase your land count too.

Tips & tricks
- All things being equal, play Mist-Cloaked Herald first over Siren Stormtamer since it's guaranteed to be able to attack.
- All things being equal, put Curious Obsession on Mist-Cloaked Herald since it's guaranteed to be able to attack. You particularly want to avoid enchanting Merfolk Trickster, Exclusion Mage, and to a lesser extent Siren Stormtamer. You'll do it if you have no other target of course, but the first two creatures can be stonewalled relatively easily, and you want to keep Siren Stormtamer available for protection if possible. If you have to sacrifice Siren Stormtamer to counter something, you lose all Curious Obsession on it.
- It may be counter-intuitive but it's usually fine to load up a single creature with Curious Obsession. The main reason to spread out auras is so that you don't get 2-for-1'ed when the enchanted creature dies. However your deck is built to avoid the enchanted creature dying, and besides you want to play Curious Obsession and connect with it on the same turn, so it's already replaced itself. Together with the point above, I'll load up Mist-Cloaked Herald with 2 copies of Curious Obsession over Trickster, Mage, even a Siren Stormtamer that's attacking uninhibited.
- It's absolutely imperative to know when to hold up countermagic. Some of the most important things to think about are Goblin Chainwhirler and the various board clears since you can't counter those with Stormtamer. Generally if you're winning, and especially if you are drawing multiple cards a turn with Curious Obsession, you want to hold up countermagic. There's no shortcut except play and learn however.
- You can lose a creature through protection if you play Merfolk Trickster or Opt on your opponent's turn, tapping out! It's not happened to me yet, but if you tap out for Merfolk Trickster and the opponent responds with Lightning Strike on your Curious Obsession'ed creature, you'll know you ****ed up.
- A few decks can directly destroy Curious Obsession. Nothing you can do about it unfortunately except counter.
- Merfolk Trickster can do things like upkeep-tap a Runaway Steam-Kin or Llanowar Elves. Yeah you probably won't be able to cast protection that turn, but if it delays them by a full turn it's still worth it. Runaway Steam-Kin is also a dangerous card because your clock is not very fast, so it can easily outrace you.
- Merfolk Trickster disables all abilities. That means it'll always be able to block Ghitu Lavarunner profitably (since it'll be a 1/2). It can even block Tempest Djinn (which will become a 0/4 non-flying creature).
- Be aware that some non-meta decks simply destroy you. Decks like dinosaur ramp for example - if they just play mana creature into mana creature into Carnage Tyrant, you're probably busted. You can't even remove their mana creatures profitably. Monoblue is very bad at playing from behind, and the only way you can stabilize a board is with Tempest Djinn. Fight hard for the early tempo. Again knowing when to leave up mana is important. You can't afford to leave protection up for your 1/1 Mist-Cloaked Herald on turn 2 for example - just play out the Nightveil Sprite. If they remove a creature, you still have the other.
- The monoblue nut draw is 2 lands, Mist-Cloaked Herald, Curious Obsession, and a 1-mana protection spell. Especially if you're on the play, you might be able to just play a turn behind the whole game.
- The turn you cast Curious Obsession is a good time to leave up protection, because if your opponent has removal they're heavily incentivized to use it.

Matchups
All usual caveats about small sample size apply. The standard gameplan is surprisingly good for most matchups, so I'll just give some cards that need to be countered (i.e. leave up mana when opponents are approaching those spells).

Boros angels - nothing special about this matchup, you play as per normal gameplan. Don't counter their small ground creatures if possible: their main threats are the big angels. Cards you really want to counter: Lyra Dawnbringer, but any of the angels is a significant threat (including Resplendent Angel if they're approaching 6 mana).

Golgari - A good matchup since their removal tends to cost a lot of mana. Normal gameplan applies. Cards you really want to counter: Ravenous Chupacabra, Vraska Golgari Queen (note a savvy opponent can target Curious Obsession which you cannot counter with Siren Stormtamer or Dive Down), Golden Demise (uncommon), Ritual of Soot

Izzet Phoenix - not a good matchup, since you can't kill Goblin Electromancer once it's in play, and it's not easy to counter (impossible to counter if you're on the draw). Still, it's not as bad as monored. Standard gameplan applies, it's just harder to pull off. Remember Dive Down lets your Tempest Djinn beat their Drakes in a fight, and that Merfolk Trickster turns their drakes to 0/4 non-flying. You can also use Merfolk Trickster on Goblin Electromancer during their upkeep to disable the cost reduction on their sorceries (they don't have many sorceries however). Cards you really want to counter: Goblin Electromancer, Crackling Drake.

Monored - a bad matchup. It's not unwinably bad, but it's bad regardless. I generally go fast and hard, you don't have time to durdle. If they have Runaway Steam-Kin into more Runaway Steam-Kin you probably lose. If given the opportunity trade your Merfolk Trickster for their Runaway Steam-Kin every time. Tempest Djinn is one of your most important cards since they can't easily answer it. You have to be careful though because if the Djinn does die, even if they have to 2-for-1 themselves to do it, you could be toast. If you can afford it (i.e. other cards like Merfolk Trickster and Essence Scatter in hand), delay the Djinn by one turn so you can protect it. Don't be afraid to counter Risk Factor; it's four damage. Cards to play around: Shock, Lightning Strike, Goblin Chainwhirler, Rekindling Phoenix (this is almost unbeatable vs. you if it resolves), Wizard's Lightning.

Monoblue - Whoever is on the play has a big advantage. Go fast and hard; Monoblue does not usually include ways to interact with the opponent. Remember you can ambush the opponent's 1/1s with Merfolk Trickster. Remember also that if the opponent has only one creature out, you can "counter" a Curious Obsession by tapping it with Trickster - since they can't attack, it falls off at the end of turn. Cards to play around: the standard suite of counterspells, and remember that the (increasingly rare) Exclusion Mage is their only real way of interacting with you.

Monogreen - this matchup is terrible if they draw their acceleration / cheap creatures and you don't have counters. If they start with Llanowar Elves into Steel Leaf Champion on the play, you might as well concede because you can't realistically beat it (you can't even chump block it). Save your counters for their creatures if you can since they're so big. If you're not holding counters then go fast and hard since their only real way of interacting is Rabid Bite and that's only common in the preconstructed decks. Aside from that the only card to play around is Vivien Reid.

Control - a good matchup. Standard gameplan. They have lots of removal & sweepers so be ready to counter. If you're able to trade up significantly on mana (e.g. Spell Pierce countering Teferi) you're probably winning. If your hand is threat-light, this is also a matchup where you can hold the creature until you can play and protect it on the same turn. Remember Siren Stormtamer can counter Settle the Wreckage.

5c Lich - only played this once but this should vastly favour monoblue. Bash their face until they hit 5 mana. They have no relevant spells until then. Just counter their 5-mana defensive card (whether it's Lich or Cleansing Nova) and you effectively win.

Bonus section
Thief of Sanity is a possible 3-drop. The upside is that it's very strong if it connects, and running black also opens up some extra card options like Kitesail Freebooter. The downside is you'll weaken your mana base by doing so, with each non-Island land making your Tempest Djinn worse. Since Tempest Djinn is your only way to stabilize a board, that makes you even worse at playing from behind. For more information see http://magic.tcgplayer.com/db/article.asp?ID=14912

Bonus bonus section
Monoblue how 2 beat?
Stack your deck with cheap removal. Removal is very effective against the deck because it really wants to play from ahead. Take for example Wizard's Retort - the card is great if you have a threat that's beating down your opponent every turn, but it's a lot less impressive if the board is empty. Without a creature on the board monoblue is virtually always losing. A cheap, preferably highly efficient threat into removal is the nightmare for monoblue, and is part of the reason why monored is a poor matchup. Monoblue can win, but not usually with the plan A of attacking with a Curious Obsession creature, but rather sticking Tempest Djinn. Some good cheap removal: Shock, Lightning Strike, Seal Away, Gideon's Reproach, Justice Strike, Moment of Craving, Cast Down. You need cheap removal because otherwise the blue deck has too many ways to trade up on tempo - getting your 4-mana Vraska's Contempt countered by a 1-mana Dive Down is a recipe for losing.

Another good way to beat the deck is to play cheap, highly threatening creatures. They don't have to be threatening in the sense that they directly kill the opponent; having some powerful effect is good enough. Cards like Llanowar Elves or Goblin Electromancer are dangerous to monoblue for this reason, as they have no way to "bolt the bird". That just leaves using Merfolk Trickster on upkeep (which has its weaknesses, e.g. most likely the monoblue deck isn't leaving up counters) and countering the payoffs (which it can't do forever).

Comments welcome!

Thanks for the effort, like reading these deck analysises.

I thought about making this deck myself given its cheapness and that I already have 3 Djinns, but I don't think I'd like the playstyle. Like being the mouse stealing 20 small pieces of cheese hoping the cat doesn't wake for the entire duration. Suppose it's natural for this deck to win small and lose big. Good thing is, a small win counts just the same as a big one.

I've lost enough times against this deck to respect it. Opponents also seem to have curious obsession in opening hand every time, which seems odd when I go through whole games without seeing my 4-ofs.
But, it's uncanny how this deck can get ahead of you (even if only slightly) and then just foil your every attempt at catching up. Reminds me of the spirits decks in duels.
It's a very all or nothing game plan, but it can get there pretty often, especially on the play.

I hate this deck. I have mainly been playing Jeskai and Golgari, and this deck seems to always have obsession T2 with protection. I mean, I know it doesn't, but sure feels that way. After 2 consecutive losses to this deck with my Golgari, I tried adding Harpooners...and didn't see the deck again until I took them out again.

The deck is strong in this meta. Curious if the deck is strong enough for people to start regularly including hate maindeck just for this deck.

Thanks for the insightful write up. I play against it now and then, mostly with my Golgari deck, and it's a bit of a 50/50. Post sideboard chances do go up when I run Duress to remove the Curious Obsession though, since without it the deck is obviously not even 1/2 as good. Ritual of Soot is also very mean against it, if it goes uncountered.

Banedon... I **** hate this deck so much!!!!!!!
that said cool post buddy

Very nice write-up! Thoughts about running Anticipate (instant speed, selective draw) over Chart a Course?

I see what you did there

I added a bonus bonus section on how to beat the deck. Kraul Harpooner is deadly against the deck, yeah. Duress I've never played against (probably because so far I'm playing best-of-1's only). The deck does have a lot of noncreature spells to hit; however, you are losing tempo by playing discard, and that's playing right into the deck's hands. I'll need to play against it to see.

Anticipate is a nice idea, I'll have to try it.

I main a Cast Down and 3x Assassin's Trophy just to get rid of those pesky monoU and UR fliers.

So far (5 Bo3 matches against Djin), Duress turned out to be my my best sideboard friend against it when I play Golgari (with Ritual of Soot a close 2nd). Almost every time I remove a Curious Obsession from their hand turn 1-2, I feel a sigh of relief. Golgari isn't necessarily focused on tempo anyway so in my experience you don't lose anything when you switch for example some 6cc spells for a few sideboard cards. Big Vraska or Carny are not very useful against a tempo deck anyway most of the time.

Duress is amazing against mono-Blue. Not only do yo get rid of the most powerful spell in their hand (oftentimes Curious Obsession, sometimes Wizard's Retort or Chart a Course), you also see every single Dive Down coming and are able to play around it more easily.
I usually side out my big Walkers and Findbrokers to make room.

Updated OP with matchup section.

- I still haven't tried Anticipate but I have been paying attention to each time I draw Chart a Course and considering if it'd be better as Anticipate. Conclusion is usually no. 2 mana is a lot to hold up; usually if I hold up two mana I'm more or less committed to countering whatever my opponent does. Later in the game, at 4-5+ mana, Chart a Course is significantly better than Anticipate.
- I increasingly think Warkite Marauder is better than Nightveil Sprite. Being able to attack into opposing fliers is a big deal.

I finally made this deck myself, just to play it a bit so I get to know it better. I have to say I agree, the Marauder has been very helpful to keep landing blows with Curious Obsession. Another thing I have found is that I lost most matchups where I did not have Curious Obsession in the early game. I've heard some people say that you have to mulligan quite aggressively with this deck, to make sure you have a decent start. Is that your experience as well? And if so, which hands do you keep, which do you ditch?

I don't have a problem to mull to 5 to get an obsession. Without it the deck is just really slow and easy to kill.

Not a fan of mulliganing functional hands for Curious Obsession. A few reasons for this. One, Curious Obsession after two hits has gained you +1 card advantage. Meanwhile you've mulliganed once to find it, so you're at -1 card advantage. So you've effectively made it so you need to connect an extra time with Curious Obsession to gain card advantage, which sounds counterproductive. Two, the deck doesn't run many lands, typically 19-21, so mulliganing means there's a real risk you mana screw. Finally, the deck also needs creatures to function. For example take this hand on the play: 2 Islands, Curious Obsession, Wizard's Retort, Essence Scatter, Tempest Djinn, Chart a Course. Do you keep?

Personally I think this hand is borderline. There's a case for keeping, but I mulliganed, because it's just so risky. Curious Obsession does nothing if you have no creature to cast it on! With this hand I wouldn't be adding to the board till turn 3 at earliest, which is very late. By that point the opponent's expensive cards would be coming online, and it's hard to pressure the opponent if you have to hold up mana.

By the way my win rate with monoblue in quick constructed has dropped to ~60% or so. Not a good sign for the deck. I'll be looking to swap especially after the pro tour this weekend.

**** Monored seriously

Like, I go into a quick constructed queue and go 4-3. Which decks did I lose to? Three monored decks. ^_______^

Dunno, whenever I play monored it feels like ****. I draw lands or no spells. Frenzy gives me 2-3 lands in a row. Maybe I'm just unlucky...

No, that would be Karma

Argh, queued into monoblue for the first time with Selensya tokens. My draw was bad - maybe should've mulliganed (3 lands, Flower//Flourish, Legion's Landing, Trostani, Conclave Tribunal). Meanwhile opponent had Siren Stormtamer into Curious Obsession. At least he was on the draw.

I spent the first four turns doing nothing except attacking with the 1/1 token from Legion's Landing, while my opponent was drawing extra cards all the time. On turn 5 I played Trostani, which surprisingly resolved. And then the game showcased one of the key weaknesses of monoblue: once a creature is on the board, it can't really get rid of it. The only ways are Exclusion Mage (in the case of Trostani, this just makes another two tokens) and temporarily disabling it with Merfolk Trickster. Opponent had three Merfolk Tricksters, but it didn't matter, since it was just temporary stalling. He was able to attack for 8 a turn but the lifelink easily kept me afloat. When he finally played Tempest Djinn later - which would've let him race - he tapped out and I targeted it with Conclave Tribunal, even over the Siren Stormtamer with Curious Obsession. Eventually an end-of-turn March forced a counter, and then the next turn I Marched again for like 6 tokens and even had the luxury to hold up two mana in case opponent had Spell Pierce (I did get pretty flooded). And now he couldn't even attack, while I alpha'ed and won the game.

After having played Selesnya tokens, I think I'd conclude that monoblue is T2. It's a competitive deck, great for budget players, but it's also inherently unstable. Fail to keep up countermagic on a crucial turn? Drawn Essence Scatter when opponent played a spell? Drawn Spell Pierce when opponent played a creature? You lose. It did go 10-0 in the Pro Tour though, no idea how that happened.

well mono blue is ok versus anything except red and selesnya tokens :-)