Penny Arcade Adventures: On The Rain-Slick Precipice Of Darkness – Episode Four Play as Cthulhu
Get the Dae-whale, then fly to the floating temple located at the southern-most area of the map, and defeat Cthulhu to unlock Cthulhu.
Play as Nigiri-Chu
Get the Dae-whale, then fly to the gladiator arena, and defeat the Fish Force to unlock the Nigiri-Chu.
Play as Ninja Z
Use the red teleporter in the third tower to reach a room with a secret passage hidden by robotic scenery. Use the passage to find Ninja Z. Defeat Ninja Z to unlock him.