The mutant in the garbage pit in the imp village does not drop anything you need, but does guard some treasure, as you found.
The mutant referred to in this topic is in a well in a small village that the necromancer teleports you to late in act 2.
I thought the problem a few people ran into with monsters not attacking was fixed in the
patch.
In a previous version there was a bug with finding the cure ingredients and moving them in your inventory before talking to the alchemist. That would trigger a quest log update prematurely, and prevent the cut scene at the rock covering the mushroom cave. There is a fix for this, however;
[*] Complete all other quests and save the game.
[*] If you have a save before finding the alchemist's ingredients and moving them, copy the 2 story.* files from that save into your latest save, otherwise you can use
these files from a save at the beginning of the imp village.
[*] Talk to Altoflix in the north of the village (if required), then the chieftain's son to get the quest to find the alchemist, talk to the alchemist once (only) and head to the cave.
[*] Continue with the game.
