We were promised that the Adapt mechanic is going to be different from Monstrosity because of counter moving/spending.
In the whole Ravnica Allegiance, there are three ways to spend or move the counters. One of them is in GR. The other two are questionably playable uncommons.
We got Biomancer's Familiar, who is obviously made to justify Adapt in the most direct and contrived way possible.
There are TWO Trample lords with Adapt, however. WHY ?? Why couldn't one of them give a unique ability... sigh. And one Flying lord, and that's all.
And, as rare Adapters, we have Benthic Biomancer and Growth Chamber Guardian, which are obviously uncommons.
Most UG cards could have just been monocolored. Only three exceptions: Hydroid Krasis, Combine Guildmage, Incubation/Incongruity.

What mechanic would you have given to the Simic to reflect their identity? Green-Blue's a trickier combination to work with; perhaps something that copies your opponents' creatures' keyword ability? I dunno though, that seems like a rules nightmare.

In all seriousness, Freeking Hosts from Unstable would be a more compelling Simic mechanic: build your own bizarre creations. Heck, maybe find a way to revisit Splice so it works with creatures, giving you the versatility to adapt your army to the situation.

I think a Simic mechanic should still resolve around +1/+1 counters. UG is a color combination of resource production, and +1/+1 counters allow you to treat power and toughness as resources. Honestly, Adapt is a good Simic mechanic, though I'd rename it to Augument or Grow or Develop. Or rather... it would be a good Simic mechanic if is was treated as one.
That said, I DO have ideas.

Enhance (, : Put a +1/+1 counter on a target creature that entered the battlefield this turn.)

Hand-Made (This creature enters the battlefield with a +1/+1 counter on it for each other card you played this turn. Lands and spells are cards.)

Incubate X (When this creature enters the battlefield, put X +1/+1 counters on it if you return a permanent you own to your hand.)

If we're spitballing, I'm going to go with hybridizing our ideas.

Gene Splice [Cost] - As a creature enters the battlefield, you may reveal this card from your hand and pay its Gene Splice cost. If you do, the creature enters the battlefield with a number of additional +1/+1 counters equal this card's power and gains this card's abilities.

Birdomobea

Creature - Bird Ooze {U}
Flying
Gene Splice (As a creature enters the battlefield, you may reveal Birdomobea from your hand and pay . If you do, that creature enters the battlefield with an additional +1/+1 counter and gains Birdomobea's abilities.)
1/1


Yes I am aware that this could cause memory issues, but this didn't even take me five minutes.

If Gene splice exiled the card from hand it would probably be easier to balance and cause less memory issues. I like the mechanic a lot.

Yeah, Gene Splice is pretty good for a mechanic made on the fly. It sounds and feels more Simic-y than their current mechanic. Its also nice and distinct from Splice onto the Arcane (something I think the Izzet should have as their mechanic - and a fine throwback to the old Izzet Guildmage combo that abused Splice onto the Arcane).

Gene splice is almost like bestow

That's what I was thinking. Could we make a version of bestow that doesn't turn into a creature when it falls off but could return itself to your hand and leave the counters behind. So you could save your flying gene from a creature that is about to die, move it to a bigger creature, or pay lots of mana to resplice it and get more counters.

Or you could make a version where where creatures become auras from your graveyard as a "gene sample" but that feels a little too Frankenstein/scavenge.

Part of the problem is just that we have 5 mechanics in one block and they are trying to dial back complexity so it is hard to make a mechanic that feels like a variant of the most complicated mechanic from Theros.

What about my mechanics tho?

Enhance is good. By itself it feel expensive to tap a creature and a mana for one counter but that just means there is room for things that get better when you put a counter on them which is good.

I don't really like Hand-Made. It does feel UG but it doesn't seem fun to me. If I was playing limited and I had 5-7 creatures with this I don't think I would really play much differently, I would just feel lucky when I happened to get 2 or more counters. It is like surge but the reward for playing 2 spells is the same as the reward for having a land to play.

Incubate is good. I didn't like it at first but it is growing on me as I think about it more. It is cool that you might not bounce something early when you are building out your board. Then when you play your big creature you can bounce the small one to get another chance to get counters when you replay it.

I like the idea of making Gene Splice as a Bestow that bounces the card to your hand instead of becoming a creature. that said, I think Adapt is a good Simic mechanic, but I agree with UC that it wasn't executed in an interesting way. needed more Galloping Lizrog effects.

I think most people would have been content if we had just gotten a green creature with something like

"When ~ enters the battlefield, you may move any number of +1/+1 counters from other creatures you control onto it. Them you may have it fight target creature."

And a blue creature with something like

" , remove two +1/+1 counters from among creatures you control: draw a card."