There are ten 'hidden' levels made by papa Blox's in Stretchmo studio five are given at the start (Sheep, Ice pop, Snail, bell pepper and red-roofed bourse) but the other five must be unlocked.

Unlockable	How to unlock
Blastro	Complete levels 31-40 in corin's fortress of fun.
Clock	Complete levels 21-30 in corin's fortress of fun.
Floato	Complete levels 11-20 in corin's fortress of fun.
Guardo	Complete levels 1-10 in corin's fortress of fun.
Moai	Complete levels 41-50 in corin's fortress of fun.