Skyfish:
Don’t fuse Skyfish with any monsters as you will need him later in the game to wake a sleeping monster.

Blankernfish:
Fuse a Cat Claw with a Wind Lord to obtain a Blankernfish.
Get the five secret monsters:
Find the five secret monsters and enter the following codes when asked
Ikonda - Password: Light
Lucifroz - Password: Dark
Pandora - Password: Megami
Chort - Password: Atlus
Starhair - Password: Tensei