There’s the level 45 talent inner demon that spawns them. Then there’s the Legendary “forces of the horned nightmare” that has a 15% chance to casts a second Hand of Guldan. There’s a chance to have up to 8 wild imps after your first HoG (2x inner demon, 6x 3 shard HoG with proc). FYI, wild imps from inner demon don’t last more than 10 secs in and out of combat. There are other trinkets and stuff that summon imps but those aren’t wild imps.