Looking a lot like Flounder from The Little Mermaid, Fugu is really a pufferfish. Fugu is the Japanese word for pufferfish.
And he can inflate in size, making him very difficult to defeat.
Since he's a fish, the whole battle takes place underwater.
Which makes not getting hit almost impossible sometimes. If you can dodge Fugu, you probably can't dodge the spiked walls. Someone tell the Kong family that if they didn't swim in the 2D plane, they wouldn't have this problem.
I never liked the underwater gameplay in the game, so a tough boss during so was not my cup of tea. I had to use powerups (first time in the game) just to win. I was glad when it was over.