Betsy

Betsy

Unlocked by completing Betsy's Challenge

Knock-Out Betsy

Unlocked by completing Boxing Betsy's Challenge

Corporate Betsy

Unlocked by completing Corporate Betsy's Bonus

Gabber Betsy

Unlocked by completing Gabber Betsy's Bonus

Warrior Betsy

Unlocked by completing Warrior Betsy's Challenge

Lifeguard Betsy

Unlocked by completing Lifeguard Betsy's Challenge

She Betsy

Unlocked by obtaining the "RAGEQUIT!" achievement

Wicked Betsy

Unlocked during Halloween

Bronze Betsy

Unlocked by getting a bronze medal on all levels

Skins written in red are not unlockable in-game.
pictures taken from Tom Rutjens's website & in-game