@Ulka also brewed up a list, and one of the cards that's on his list is
Spider Fog, which I now have to add.
Out:
All three Guildmages - too limiting, too fragile, and too expensive to use.
Naru Meha - I don't want to pay 4 for a fork with a body.
Bonus Round - Tough call, but I feel like this is wishing for Magical Christmasland to happen. I have it, AND the spell I want to copy, AND a spell to copy it, AND eight mana. And the end result is ... 4 of that spell? Okay. Other people probably wreck worse when I cast this.
Radiate - I just don't have single-target stuff. It's really cute, but not in this particular deck.
Mirari - I'm spending a turn on this, and I don't know that I like that.
IN:
Arachnogenesis to make a ton of tokens
Destructive Revelry to deal with problematic permanents
Ezuri's Predation the one time where Forking a Wrath is a net plus
Nucklavee to get things back
Vengeful Rebirth both to get things back and to go to the face
I dunno, two more rocks? I want to up my artifact count and I'm realizing how much mana I'm going to be spending all at once if I want things to really copy copy copy.
I decided against the acid-moss or the ting in the end, both because I don't want to be That MLD Pilot, but also because my current playgroup doesn't have lands that need to be answered. Nobody runs Academy Ruins The Game, or Volrath's Stronghold, or Gaea's Cradle. If people start deploying them, I'll rotate in some answers, but for now we'll call it a meta decision.