See Peculiar Distortion.

This was originally going to be a U Turn to Ape, but I decided that trying to have a mana discount AND a different colour was too fiddly, and black could do "destroy creature, give you replacement" as well.

Odd. There are time you want to turn to Ape, but most times you just want one or the other mode. Perhaps give a Sleeper Agent instead?

I'm sure that makes sense but I don't quite understand what you think.

The advantage of turn to ape is that it's 3 mana cheaper.

Sleeper agent only makes sense if you have to give it to opponent. If you're only using one mode, you get the 3/3 yourself. Is that not sometimes useful for 3B?

Hee. This is entertaining, yes. It's basically Feast or Famine, but you can get it "cheaper" (still needing 4 mana up front) if you don't mind using it as Pongify. I could do something similar on Peculiar Manhandling and even Peculiar Annihilation.

Do you need the mana up-front? I thought you paid the costs at the same point in any order, and could choose to pay the "add 3" before the "pay 3B". But that's the sort of subtlety in the comp rules I find really hard to get right!

Ah! I could use megatwine to clear up the mana cost. I made up that keyword for another peculiar card, the intent being, "cast for this cost instead (not as well) as its usual mana cost and use all modes of the card". But I didn't think it was very cheaty since it seemed like it would have been a reasonable way of writing entwine.

But it simplifies peculiar spells where the combined mana cost should not include the original colour, or should be cheaper -- here it could be "mana cost 3b" "megatwine U" where casting BOTH is a disadvantage. And the same for peculiar manhandling.

Cards like peculiar annihilation are trickier because the original costs aren't balanced, though you could maybe do something like.