A character gets attacked by a Wight on the Tomb card and successfully kills it.

He has a Warlock Quest to kill a Spirit (which is what the Wight would be if it was encountered as a card).

Is this considered completing the quest or not?

That would be a great assumption.

The "Spirit" required by the quest "Kill One Spirit" is an "Enemy-Spirit" as defined in the basic manual at page 7 under "Types of Adventure Cards".

This doesn't include the Spirit in the Crags, or anything that might be associated with spirits in general, but it's not an "Enemy-Spirit".

Thought that might be the case, considering the Crags topic I raised last year.

My friend and I decided that defeating such enemies at the Tomb was considered killing Spirits, but we will now know in future that this is not the case.

Would the Merchant be able to pay off the Cave Troll in the Ruined Mine space of the Highlands? Would it regenerate? Or would the Dragon Rider be able to ride the Cave Dragon? Would the Vampire Prince encountered by rolling on one of the Blood Moon cards kill a follower?

It's a trouble with using creature names that also are Enemy names. I say if you can't apply all cases, don't apply any case. agreed with Warlock!