Enter Finnius, Frogger, Frogger, Wani as a password.
Baseball Cap
Enter Frogger, Frogger, Frogger, Berry as a password.
Bunny Ears
Enter Lily, Frogger, Frogger, Lumpy as a password.
Camouflage Costume
Enter Lily, Wani, Lily, Wani as a password.
Cowboy Costume
Enter Frogger, Lily, Lily, Lily as a password.
Croc Hat
Enter Lily, Lily, Wani, Lumpy as a password.
Mohawk Wig
Enter Berry, Lily, Lumpy, Lily as a password.
Pirate Hat
Enter Frogger, Berry, Finnius, Frogger as a password.
Santa Costume
Have the Game Boy Advance game Frogger's Adventures: Temple Of The Frog in the cartridge slot.
Santa Hat
Enter Lily, Lily, Wani, Wani as a password.
Unlock hidden Costumes
While playing "Frogger: Helmet Chaos" with one of the following GBA games in the second cartrige slot you will unlock hidden costumes in the "Costumes" menu.
With "Frogger's Journey:
The Forgotten Relic" you get the "Punk Costume"
With "Frogger's Adventures 2:
The Lost Wand" you get the "Pirate Costume"