I figured, why not discuss potential ideas for alt rounds before submitting them? That way we might have less accidental boring rounds.

I thought of one today that might be fun, but it makes the symmetry checker useless and may not be worth the extra time.

Dibs!: You always go first.

So basically, if you had Swamp, Funeral Charm, Diregraf Ghoul vs. Black Lotus, Black Lotus, Grave Titan both decks would score 6 on their round. When Charm is scoring their round, they go first both games and force a discard then walk to the win. When Titan scores their round, they go first both game and Titan comes down for the win.

I find alternate rounds to be the most interesting when they open up territory for deck building. Dibs doesn't really do that, or if it does, I don't find it's method that interesting. There are already plenty of standard 3CM decks that rely on being dominant on the play and just hope that the meta is slow. Dibs would basically just limit your deck options.

In general, improving mana options does a lot to change the format. Almost every format like that has been dynamically different than Vanilla, which I think should be the main goal.

Changing game rules varies wildly on how a big an impact is created. I tend to think they don't do good enough a job.

Looking at the current options:

3 New Design Paradigm: Creatures cost less to cast. Noncreature spells cost more to cast.
The restriction on noncreature spells is a way to force people into utilizing the creature cost discount. It's very "format-crafting", but I like it enough. It's too easy to avoid round rules too often.

4 Endless Ones: At the beginning of your upkeep, you may exchange any card in your hand with an Endless One from outside the game.
This just doesn't do anything useful. It influences you to play charge lands, but otherwise, it's not an interesting idea at all.

Memento: Players start with a Memento artifact card in hand. It costs and has Squee, Goblin Nabob's ability.
This offers a lot of subtle deck-building decisions. It's a neat way to emphasize that you don't have to give players a lot for real format changes to occur. It might actually be a moot point, though; I can see this format being the victim of "I played BridgeTongs/Titan/LeylineKarakas, your cute Memento deck does nothing." But that happens sometimes.

Berserker: Creatures can't block. Combat damage can't be prevented. Prevent all non-combat damage that would be dealt to players.
Seems pointless. If your deck would block, chances are you're just gonna win attacking anyway. It doesn't actually change much to the way you'd build a 3CM deck, which is a sure sign that it's not much of an alternate format.

Spirit Guides: Each card has "Exile this from your hand: Add or one mana of any of this card's colors to your mana pool."
There's very little chance that this has merit. Even if there's a deck that can utilize this, it's one deck out of many, and most 3CM Vanilla decks are gonna come to the program as is. In fact, the decks that generally gain the most from this are those that already use Spirit Guides.

2CM

1CM

forget that, go all the way to 0CM

I think rounds that encourage new deck building strategies or twist typical meta analysis in an interesting or trappy kinda way are the best. Dibs does the later. Discard and/or control seem significantly more powerful since their plan always works, which encourages decks that aren't prone to lose to discard. Although Titan would still probably sweep the round, the meta could swing different. It's less of a guarantee than usual.

As for the current choices, I agree with your analysis except for the Spirit Guide one. It gives a turn 0 Funeral Charm, Mana Tithe or Force Spike which is probably relevant. Although this season it would simply be Vanilla Round 3 since FoW is legal.

I thought of a dumb one that people would probably love:

Alphabet Soup: At the beginning of your first main phase add one mana to your mana pool of each color card names in your deck could spell.

i always wanted to add purple mana to my mana pool

oh wait i still couldn't, curse the rules getting in the way

Screw the rules, go for broke. I was looking forward to adding orange

Edit: Oh yeah, and it would be EACH first main phase.

My logic on what might make Spirit Guides different:

1. T0 disruption. The fact that there usually isn't a Black/Blue/White spirit guide option means that the usual T0 disruption duos (Piracy/Funeral charm, ForceSpike/ManaTithe) aren't in play. They are here.

2. An 'option play'. You could play something like Black Lotus, Ajani Vengeant, Windborn Muse, and at play time based on what your opponent's deck can do, your deck would be able to decide whether to play in planeswalker mode or creature-combat-prevent mode.

3. Just squeezing more mana out of cards that have their utility without leaving your hand anyway - like Chancellors.

(A combination of the above allows for a deck like Funeral Charm, Mesmeric Fiend, Chancellor of the Forge to exist. On the play it Fiends out an opponent's card and has two attacking threats. On the draw it T0-disrupts instead.)

Ya, the spirit guide format has more merit than I claimed. It's got strategic depth, which is nice.

Commander 3CM: Technically 4CM because you're choosing a Commander in addition to your three-card deck, but otherwise follows the same rules and setup as Commander (40 starting life, 21 points of combat damage from a single Commander makes you lose the game, singletons only except basics and cards that say you can have any number of them in the deck, color identities of cards in deck must conform to Commander's color identity, etc). In addition to the standard 3CM alternate round banlist and Vintage banlist, this follows the Commander banlist (so no Karakas, among other cards that typically see play in 3CM).

I don't know if any previous seasons have done this, but it seems like a fun idea to me.

I was just thinking about this earlier today too, actually. Could be fun.

I would totally expect somebody to run Black Lotus, Lion's Eye Diamond, Lotus Petal/Command Tower and just drop their 7 cost Commander on turn 1. Alternatively, use Omnath, Locus of Mana as their Commander and build up as much green mana as they could to (potentially) get a fast win.

black lotus is banned in commander (for price reasons of course)

however, mana crypt, mana vault and led aren't, so some version of the all-in strategy would be around

Trigger Happy
All triggered abilities you control trigger at the beginning of your upkeep in addition to whenever they normally would trigger.

That one seems fun. I've been working on these three lately, but I feel like they need something...

Empty Promises: You have no hand size limit. At the beginning of each draw step create a blank card and put it into your hand. (I want to enable hand-size matters without reverting to the Limited Mill or enabling "whenever you draw a card" plays)
Kevorkian's Nightmare: Permanents can't be sacrificed (this one doesn't seem to make a significant change from vanilla)
Mindslaver: You may choose one turn after your opponents first turn in which you control your opponent (just really weird to try and work out)

For Empty Promises, I'd change the card to something you can actually use, like Wastes.

I agree about Kevokian's Nightmare... somewhat. It'd enable Phyrexian Dreanought tricks. The sad truth, though, is that it'd be best in Leyline of Singularity/Karakas/Phyrexian Dreadnought.

Optional Mindslaver feels like a lot of debating over when exactly is the best time to control the opponent. It might not actually be that bad, though. I've seen "You control your opponent during your turn" work out. That I thought was a neat format.

empty promises would probably be more interesting as backbuild

Hmm, why do you say that?

@Rush: You think so? The last thing I want to do is just have another Admonition Angel round. Although playing with the concepts in Memento I agree that expansive changes should encourage more than one or two (viable) new decks. Maybe we could merge the ideas and each turn you could create a Memento. It would expand on the Artifact matters themes of Memento and also potentially enable some REALLY clever hand size matters decks.

the general issue is that most alternate rounds don't pro-actively discourage traditionally powerful strategies (whether that's the different banned lists or the fact that the concepts don't go far enough or some combination of both, i don't know) so the impact would be felt more in a backbuild round (considering that makes some of the go-to decks far worse)

obviously the card would have to do something other than be blank, otherwise that's not opening enough design space (if it's a land then naturally lotus should be banned if it's not backbuild, otherwise you're not really encouraging the round theme)

i'm having a similar issue with the memento round, anything i can think of that is potentially interesting is superseded by already-known strategies