Terrible and Evil doesn't let you choose a minion to wound if his vitality left is other than number of times Gandalf exerted - any minion should be possible to choose.
To be honest, I'm not sure if you should be able to choose a minion with less vitality than the X chosen to damage it (I assume you're doing it because of damage prevention available, like -
Hides). But for now, that's how it gonna be - you WILL be able to choose a character with less vitality than X, when instructed by game/card to wound character X times, as long as it can take wounds.