Here is the full list of all 22 Chipmonk! achievements.
Complete Classic as Grey.
Complete Classic as Cheeks.
Complete Classic as Red.
Complete Classic+ as Grey.
Complete Classic+ as Cheeks
Complete Classic+ as Red
Defeat 800 Mice.
Defeat 1,000 Club Rats.
Defeat 1,500 Spear Rats.
Defeat 200 Porcupines.
Defeat 200 Raccoons.
Defeat 1,000 Beavers.
Defeat 350 Moles.
Defeat 200 Red Squirrels.
Defeat the Gray Squirrel 50 times.
Collect 300 Cherries.
Collect 2,000 Special Fungi.
Defeat 100 Frosties.
Collect 50 ? Fungi.
Rank on any leaderboard.
Clear Revengeance as any character.
Collect 100 extra lives