2023-04-14
If you choose two target creatures, but one of them is an illegal target as Wicked Slumber resolves, the illegal target will be unaffected. You'll put both stun counters on the remaining legal target. If both targets become illegal, Wicked Slumber won't resolve at all.
2023-04-14
The two stun counters can end up on the same creature, or they can each end up on a different one of the target creatures.
2023-04-14
Wicked Slumber can target creatures that are already tapped.