Just as with Depths of Desire, if you dont disable Karn’s Temporal Sundering, it will go off and you can choose Not Now but it will cast anyway and give you the extra swap without bouncing a creature.
I’m considering this a feature, not a bug. With Hazoret’s Undying Fury, Pyromancer’s Goggles and Karn’s Temporal Sundering as the only other spell, you can easily get 10+ extra swaps each turn and changing this would make this combo impossible.
So please, let Karn’s Temporal Sundering be cast even in the future when the opponent has no creatures.
Let’s not and say we did
Wait. Temporal Sundering return creature (note: it’s not opponent creature ). As so you may cast it to return your own to get additional advantage)(like extra swap is not enough advantage)
Yes it works as you said returning also your own creature.
Another great feature is that if the hand is full the creature is destroyed as when using Claim with full hand.
I think this is a feature, not a bug.