The Colossus (or Dreamy) is the final boss of the Shadow Arena
Colossus will always have at least 1 passive buff, and can have a max of 3 buffs,
Colossus' strength varies based on the Uber arena level.
Colossus' buffs and tips:
Teleport - Teleport is the hardest buff to deal with, as he can teleport to anyone on the Arena, so I recommend you to group up your team in one point on the arena, them everyone can hit the boss and kill him fast.
Bee - The Bee is the most useless buff for Colossus, as the bee have a low life and damage, as it don't scale with the arena level as well as the other mobs, so you can kill it very fast.
Poison - The Poison buff allows him to use the poison bomb, the same from the purple mushrooms, so you need to avoid this poison at any cost, because it deals a percentage of your health (probably something around 20%) as damage, and not a fix quantity, like 1k for example.