Random Generator gave me Solemn Offering and Lava Hounds, and I fear I dropped the ball a little. Those cards just do different things, and I didn't want to take two simple cards and make one confounding card with four random R/W abilities. I tried a number of things, including a Nightmare, but nothing felt right. In the end, I landed on an ability I'd like to see on a few more cards - surpise commando for just this turn.

Well, at least you got the total net lifechange to yourself equal to the total of those two cards... Yeah, that's an odd pair.

Perhaps something that's guaranteed to affect your life total by 4 one way or the other? Or a coin-flip card for whether you gain or lose life?

Creature - Elemental, 4/4, (edit: or )
Haste
[When ~ ETBs,] or [Whenever ~ deals combat damage to a player,] or [:] Destroy target artifact and flip a coin. If you win the flip, gain 4 life. Otherwise, ~ deals 4 damage to you.

I would have been so tempted to make "2RRW. Haste. When ~ comes into play destroy target artifact or enchantment" as a literal combining of the cards, but I agree that's not actually very interesting.

I like your version, turning "when this comes into play" into "when this deals combat damage to a player" on a haste creature is an interesting move. I was going to say I don't think "haste" and "sacrifice at end of turn" are green-common, but then, I guess groundbreaker had them in planar chaos shrug

(You could probably remove the sacrifice clause if the creature wasn't common -- green does get ridiculously good creatures.)

The coin flip option is clever. I don't know if life gain is ever red, for but it would be a good excuse for a R/W card. Every time I work this card, though, its the Haste 4/4 that keeps hanging me up. I want the card to be a powerful hasty creature, and then I want it to gain 4 life. The combination just doesn't come together easily.

I was going to list a few creatures that have haste in green, but its actually too long a list to bother with. It doesn't happen often, but it does happen.

Re: haste: I was basing my opinion on http://gatherer.wizards.com/Pages/Card/Discussion.aspx?multiverseid=5555, where MaRo says black gets more haste creatures, but green gets more constructed-quality haste creatures. So green definitely does get haste, but so far only on splashy uncommons and rares, and in planar chaos. Maybe green will get common haste eventually, but it doesn't sound like it's likely to get common haste with an ability as well?

Re: lifegain. Red never normally gets lifegain (?) but I think as a coin-flip result is probably fine.

See, this is one of those combinations where I want to have multiple cards inthe design file. I think I might keep this Centaur and add something that spins off the +4, -4 theme as well. Its odd. I know I'm just making the rules as I go along, but there still seems to be some rule in my head that says "only one card per match". Still, in the end, I'm going to have double the cards needed to make a set, so having both versions of a card to choose from will be advantageous.

On a side note, if they do make a Green haste common creature, I doubt it will just have haste. After all, black has a number of commons with Haste, but none of them have just Haste.

Yeah, I like the different possible versions too.

WRT Haste, my best wild guess would be that since red gets small vanilla creatures and high-P low-T creatrues, and black gets small creatures with something else (flying, shade +1/+1, infect, etc), green would get medium-to-big creatures, possibly with trample. Probably just one at first. I'd still guess simple, but you're right, they'd probably have something extra. But I do love this card, but I tend to think either "4/4 haste uncommon destroy target X" or "4/4 haste common" would stretch it enough, both may be too much on one card :(

ETA: Come to think of it, now green gets haste, flying AND intimidate. I wonder if it will ever get all three at once? :)

Naturalize Slot.