Hmm. Some good arguments made for mulligan. Rethinking it, they are probably right.

You have 53 cards left in the deck (6 in hand, 1 known)

You have 16 cards you would prefer to Abrade for T2 play.

That gives you a 30% chance you will get a better card if you scry to the bottom and an about 70% chance you will either maintain or worsen your draw.

I would keep. The mull makes me think he is agro. If he is control, he is less likely to go to 5 even if he has a substandard 6 card hand because you can't give up too much card advantage as control, so him keeping it does not mean he has a good hand.

Basically, I think the odds are better that your Opponent is NOT a well stocked control deck than your Scry will get you what you need to beat your opponent if he is a well stocked control deck.

I’d keep

On the play I would keep, on the draw mull.

That's a rough one. I'm thinking mull because of the difficult decision your 4 cmc play is. Other than that....

why would it be difficult? The board state would clearly favor one over the other

Well I was just saying I would prefer to curve than wait until 4cmc board state to make a decision. That's why it's a back and forth as to weather mulling or not really. I still think I would mull for that reason.
Remember, I'm a horrible player.

The mana is just too good and you get Chandra on curve. If the deck is built right, you're bound to pick up an early drop. I dunno, for these situations i gotta have faith in the build and that it will come out correctly

Just from my experience lately playing vs r/b with mono green: If they play soul scar on turn 1 then I'm more likely to lose than win, if they play bomat I'm pretty happy. If they do no plays on turn one or two then, assuming my keep was good, I'm probably at 90%+ to win the game. The strongest cards in the deck are one drops (imo) and while pheonix is a great card it's way too slow to be a first play (that's the turn where I'd want to be dropping ghalta on the table).

Maybe you're right though, I might be underestimating the value of having a bunch of lands in the opener since at the moment I'm very used to a deck that needs 3 mana to cast almost everything, certainly with a control deck I'd keep a 6 land hand in the dark, but I just don't think an aggro deck can get away with such a hopeful keep. Maybe 1/3 games in quick constructed seem to be mono-red flame or r/b, I feel being slow is pretty suicidal.

Yeah those are good points. I have zero experience in Arena so its obviously very different to what i'm used to pulling off in Duels

I guess it would be with the rarity rules. I'm not even sure what they are. I played Duels for about a week in total and never even got beyond the tutorial quest thing.
What was it? One mythic or somesuch? If that was it then yes Arena is WAY different. Having 4 Rekindling Phoenix's as opposed to one would really make you rethink the deck.

yeah, one mythic. So if you draw the only copy of Chandra and Pheonix and in your opening hand and the mana is good... well...you keep

You're playing R/B aggro against a UB control deck.

Your board is Rekindling Phoenix and Scrapheap Scrounger. You are on 14 life. You have five lands in play.
Your opponent's board is a tapped The Scarab God (a zombie since it was resurrected by Liliana, Death's Majesty). His graveyard contains a Torrential Gearhulk, a Fatal Push, a Champion of Wits, and a Doomfall. He is on 9 life, and has six lands in play. He just passed his turn with an attack and no play.

Your hand is Chandra, Torch of Defiance, Scrapheap Scrounger, Abrade, and Glorybringer.

What's the play?

I think Glorybringer will likely drop the opponent life to small enough that chandra wins next turn so i would do that cuz hes going to fatal push scrounger and prevent lethal this turn. I'd be tempted tho to maximize value and play chandra and scrounger but i think he kills chandra that way which leaves me less options for victory? The big question is who do you rather hold up in hand for next turn, chandra or Glorybringer?

That's my thinking as well, just slam damage and try to pull him into burn range.

I have a few thoughts, too:

Going against U, I always expect counters, but in this case his options are limited. If he taps to counter whatever you play, your Phoenix will probably survive - worst case being a 2cmc counter and then the 4cmc exile. If you force a 3cmc counter, he can't bring back the Gearhulk with the Scarab God, so he untaps with 5 power instead of 10.
Which counter is more probable to face? 2cmc creature or 2cmc non-creature? I don't know that. But I'd guess Chandra has a better chance of a) not getting countered at all and b) the counter being > 2cmc. Syncopate also takes 3 because you'd have 1 mana left to pay if he didn't pay 3 for X=2.

But despite all that, if your spell resolves, you'd much rather have the Glorybringer for 4 damage now and lethal next turn. Chandra does what? She dies next turn anyway if you don't switch to defense and keep the Phoenix as a suicide blocker. So from his PoV, I'd maybe not even counter her, but counter the Glorybringer.

Another thought, that might be under the radar: Abrade kills the Gearhulk because he is an artifact. So you could play it slow, only attack with what you have and when he taps to bring him back, you just kill him again.

In that case he untaps with 5 life (edit: wrong, should be 2 for he can't block the Scrounger) and 6 mana. He could tap for whatever, do whatever, but I don't see how he would kill you. In that case you just play Glorybringer (edit: or Chandra or nothing) for the win. If he just passes his turn again, you'd face the same situation minus Abrade plus another card and him at less life.

I think, I like this last option best.

edit2: later
I see that his Vraska's Contempt spoils that plan..
Well, I just don't think you had much of a chance against Contempt + another Gearhulk

edit3: The original edit was stupid
On double-checking I forgot that the Gearhulk would still fetch Fatal Push to remove the Scrounger before it can swing. Good thing most of you are still asleep so I can fix it in time.

Depending on the UB build he might not be running many counters at all, maybe only supreme will. Given that there were none in the graveyard I probably wouldn't play around a counter there. I'd cast glory and swing out, while cursing being on 5 lands not the six needed to kill the scarab god for a couple turns.

Eh, even with 6, I think just going face is probably best. You're nearing the point where he will take over so you gotta do everything you can to get into "topdeck a burn spell that just ends it" range. Delaying Scarab God doesn't help much if you're not in a position to end it.

Well, you still go face, just exert glory then abrade in end step. With a contempt in hand he just exiles pheonix, takes a net of 5, then he has gearhulk flashback contempt next turn for 4 mana to pop the glory and the following turn he attacks for lethal. Though this all revolves around him having contempt in hand and us having 6 mana, so yeah, not exactly relevant

Keep or mull? 4 Mountains, 1 Aether Hub, 1 Bomat Courier, 1 Kari Zev on the play vs. unknown opponent.

I mulliganed that hand and drew into 1 Swamp, 3 Mountains, 1 Canyon Slough, 1 Abrade. Keep or mull to 5?