Wait, wait...

A becomes B, and B becomes A. Then you swap control - so the controller of A now controls B-that-is-now-A, and vice versa and did we jut do a lot of work for no net change?

This feels like a card I'd make to be silly. What's it for?

I guess it kinda sorta matters if one is enchanted or has counter on it?

If one has something attached to it, counters on it, continuous effects after layer 2, another spell or ability on the stack targeting it, or if they are in combat then this can remove them from combat, if one leaves the battlefield and comes back, if something cares about owner, etc. There are many, actually. Note that their controllers need not be different to cast this spell; it can be cast on two permanents with the same controller or with different controllers. Also, their status is not exchanged; if one is tapped and the other is untapped, B-that-is-now-A is now what B was tapped/untapped rather than A, and if one is face down, even though it copies something else, it is modified by its face down status so the values it copied are ignored until it is faced up. Initial text is not (and cannot be) exchanged. Kind (card or token) is not exchanged.

Yeah, this is bonkers in a flicker deck. My fatty becomes your land and your land becomes my fatty; then we swap so I still have something that's my fatty and you have my-fatty-that's-become-a-land; and then I flicker out that thing and it comes back as my fatty. Except most flicker effects can't actually flicker lands, so I guess s/land/weenie/. And it only works with offensive flickering, which is the minority of recent flicker effects... OK, maybe not really bonkers.

I mean, that's what Gilded Drake is for in my Roon deck, and it is in fact bonkers

The counters thing seems to be the easiest to put together for maximum impact. Just target a creature your opponent controls with +1/+1 counters on it, and exchange it with a permanent with -1/-1 counters you control. Presto bingo, advantage.

But yes... a bit of a mindwarper.

Gilded Drake plus flicker just lets you steal the best creatures at the table though. I don't think even if you had a way to loop this card and a repeatable flicker effect it'd do that.

I think power-level-wise this seems okay at about or some such. Comprehensibility-wise, it's of course going to be a huge red flag :)

This can be used as a pseudo one-shot activation of Bazaar Trader, too, right?

As an instant this is also a form of counterspell/hexproof/reroute. Imagine casting this in response to "Destroy target permanent."

And then, what will the name be?