­Silvergill Adept + Dervish Scimitar (Which is itself a mash of Dancing Scimitar and Mogg Sentry

So a big "Play merfolk" build hint, an animated artifact, and something that punishes the opponent for playing spells. (But not too hard, because, well, what else is your opponent gonna do?)

Well, merfolk already have some "Mess with opponents spells" wizards, so some kind of artificier makes sense?

First attempt: ": Next time opponent casts a spell, put a +1/+1 counter on something" Mechanic isn't really fitting for blue - it'd rather give out special powers.

I reckon we can do that - give them +1/+1 and Islandwalk (the counter being a neat way to mark the islandwalk)

Is too aggressive a cost? I don't really want to bump it to 4. Let's try .

I'd rather see "Whenever an opponent casts a spell, you may pay . If you do, put a..." That way you don't confuse people about whether this works if you do it in response to a spell, or they cast a spell in response to this ability. (In both cases it doesn't work which is another reason to use the triggered wording which does.)