How does one obtain a Witcher 3 Troll Mutagen from a non-quest specific troll, at least one of which you never exchange dialogue with?
Solution 1:
The best way to get one is from the rabid rock troll on An Skellige. It spawns next to the fast travel point Trail to Yngvar's Fang which is Northeast of Urialla Harbor. It respawns, i got my mutagen after 5 kills.