Yoshi's Island: Super Mario Advance 3 Cheats

When entering the arena, do not pass the end of the stone colonade that is at the very edge of the large arena room. This will allow you to see the small pirhanna plant without activating the boss battle.

From here, you can fire an egg at the pirhanna plant and destroy it with one hit. This forces Kamek to appear and say 'OH MY', before fleeing. Having already destroyed the plant and scared Kamek, you will not have to fight the Naval Pirhanna, thus avoiding a potentially difficult boss battle.