Secret Island is the final level of Viggo A Gogo. It takes place on an island where Viggo's lair is hidden. The main objective is to go through a bunch of trials to eventually battle Viggo. Each trial requires the use of every Fur Fighters special skill to proceed. The final Flea Mini Game is also on the island for Rico.
The first trial involves Chang. He must defeat four of Viggo's cage guardians (Uber Bear, 31st Century Fox (mark II), Odebah Bear and Oddfelt) and disarm the weapons and ultimately free himself from death.
The second trial involves Rico. He has to chase General Viggo's pet human, Fifi, and take the key from him to get out of the water garden. There are also piranhas in the water that take on the form of the ordinary fish you usually see in a fish tank, and will deal quick, consecutive damage (roughly the same speed of standing on Chang's pit of lava upstairs in his house) to Rico if he doesn't get away fast enough.
The third trial involves Juliette. She has to fight 100 bears, with 90 Brown Bears at the floor level and 10 Blue Bears at the next level. There are 3 boxes at the floor that spawn 3 bears in each box. Each also have their own powerup (Meerkat Multiple, Beetle Shield, and Bear Disguise).
The fourth trial involves Bungalow. According to General Bristol he is "too stupid" to fall for the Fun House's hypnotic spell. He must defeat Mr Grr and Mr Arr before the Fun House's deadly hypnotic trance destroys him (indicated by a timer). The timer can be reset by touching a bell in the center of the room, which clears his head.
- Blue Bears (12)
- Brown Bears (113)
- Polar Bears (5|1)
- Panda Bears (7)ꜟ
- Crocodiles (3)ꜝ
- Peacocks (2) ((Dreamcast only)
- Armadillos (6)
- Shrimps (1)ꜝ
- Foxes (6)ꜝ
- Grondas (5)
- Chameleons (8|6)
ꜝ Excluding Viggo's Revenge
ꜟ Viggo's Revenge only
- Every standard enemy from the original games is present in this level.
- This is the only level that is possible to make the Chameleons fall in the water by making them follow you to Rico's trial.
- Several minor areas have been removed from the Dreamcast version of the game, resulting in a shorter level.