So hey, unsummon is surprisingly abusable with ETB triggers. Let's focus on that, and save the cost of recasting, shall we?

Not so helpful on the defence, mind you. (Also, despite being small and simple, probably unprintable at common; due to "I target this creature in my hand! Graveyard! Deck!" Maybe adding the explicit "Target creature on the battlefield" but then you hit the whole "But, uh, why bother?" barrier.)

The explicitness is already made clear by the use of the bare word "creature" rather than "creature card".

And would this call for a new rule, analogous to 400.8, that says moving a card from battlefield to battlefield makes it a new object? If so, this is functionally identical to a flicker effect (unless you have some weird card like Goatcloud Stranger going on).

I intend this as "Trigger ETB effects" really; I kinda expect it to not trigger LTB ones. I know that the "target creature" works as intended; but it seems likely to be rejected as "This will confuse most people, and even after it stops confusing them they'll hate it"

Yeah, this is just Cloudshift but more confused about whether it makes things leave combat and suchlike.