Elusive 4 achievement / where can we find them / post pictures

[Haligali]

These bosses will spawn after a specific type of mob is killed.

not after, instead. don't need to kill to spawn them.

I see people running through the maps not killing anything. Do I really need to kill mobs for the small boss to spawn or is he already there?

thats right, just run through the map and check the specific mobs.