kickiluxxx wrote...
Ok, now, let's say that happened and I only have 1 creature that is now hexproof and no other permanents in the battlefield but lands. Does my opponent have to exile his own creatures then because he already casted O-Ring?
No, the ability fizzles as it's target is no longer valid.
Speaking of Oblivion ring, here's a neat trick you can do with it
This requires AEther Vial on 3
1. Cast Oblivion Ring
2. With the exile trigger on the stack, activate Aether Vial putting in
Flickerwisp
3 Target Oblivion Ring with Flickerwisp
4. The second O-Ring Trigger is now on the stack, because the stack operates, first in, last out, the second trigger will resolve first, but it will return nothing as it hasn't actually exiled anything
5. Resolve the first trigger
6. End turn, O-Ring returns, exile another thing
Congrats, you've exiled two things with one o-ring.