Here is the full list of all 31 Frogun achievements.
Beat Beelzebub
Win all races
Get all health upgrades
Beat Hexy
Beat Scorchy
Beat Wintry
Beat Kicky
Defeat a boss cosplaying as them
Own the Kiwi and Melon hats
Finish a level without damaging any enemy
Get a Max. Health Up
Beat Prickly
Pose for the camera
Take a photo of the scenery
Hit Jake with something during a race
Buy a hat
Win a race
Fall on water
Finish a level under the time limit
Finish a level with all of the emblem pieces
Finish a level without dying
Finish a level with both eyemeralds
Finish a level having found the notes
Finish a level with the obsidian skull
Get all coins in a level
Get all of the complete emblems
Buy all hats
Buy all gallery images
Complete the bestiary
Beat the Boss Rush
Beat the Brutal Rush