Flappy is a slightly bad-tempered pike that behaves similarly to Porpoise. Fans refer to it as "Flappy" though it may not be his official name.
He is usually a blue, turquoise (in some releases), and green fish with fangs, sharp teeth, and fins that turn into hands.
In the Tom and Jerry Tales episode "Over the River and Boo the Woods", he is actually dark grey with red fur and with black devil horns.
Tom and Jerry
Tom and Jerry Tales
Flappy chasing Jerry as he tries to catch him with his teeth.
Jerry squirting Flappy with a lemon
Flappy about to catch Jerry
Flappy staring at Tom in anger