Currently, targets for objectives like kill, use-emote, etc. can only be used once "per GUID, per objective". However, some users would like to make a quest to kill/emote the same Player several times.

Since Player GUID never changes, this is impossible under the current system. While I would like to split up Create/Player targets in the future, for now I will just allow Player targets to be used multiple times for any objective, while leaving the "unique GUID" rule in place for Creature targets.