I'm level 6, ennemy goblin is level 1.
I enchant him (not sure the name in english ... the priest spell that makes ennemy turn against its friends for some time).
When the spell wears off and he becomes again an ennemy and my creature kills him I get 0 xp.
When I directly kill a level 1 goblin I get 1xp.
Imarion
PS: 1 xp is nothing but I wonder for later in the game.
