I just got owned by a red color giant Ice slime Named Guardian of nix ! Is that a random spawn ? I didn’t even make a dent in it. 
Legendary creatures will spawn after completing the feat for killing 50 epic creatures. Idk if they can spawn otherwise, but I’ve never seen one other than from the feat completion.
What do they give you? Anything special? Because I found one to I died 2 time and it didn’t give me any thing good.
Random loot no specific…sometimes I could get legend item,higher class of crystals and myth stones.
Ok, that not so good I thought that it could of dropped one legendary at least and maybe some high class crystals or mythstones.
I think a mythic creature drops a high mythstone
Yep Bole you’re right…I looted 2 level 16-18 myth stones in a single mythic enemy it happened to me only once at version 1.7.0…