In order to train Colossal, you must have previously trained Strong
, Giant, Monstrous and Gargantuan
from the trainer located in Celestia Floating Land.
You must reach Drum Jungle in Zafaria before the quest to unlock the trainer obelisk
will become available. The quest to unlock the trainer is given by Inyanga Whitestripe
located at the Baobab Crossroads. The quest is called Bungle in the Jungle
and it directs
you to speak to Koko Smokesign
You will be unable to speak to Koko about Bungle in the Jungle until you have completed
the quest called For my next Trick
which directs you to fight Shadow-Weavers for
The quest to unlock the trainer is called Midnight Sun
& requires that you fight Black Tusk Cultist
for obelisk pieces
I hope this helps!