Complete each achievement to get the allotted gamerscore.
Unlockable How to Unlock
The Inflatable Reptilian Hero (5) Get flattened by any trap.
Seen My Bones? (5) Get zapped by any laser traps or attacks.
Invincible (5) Complete a level without having to use a single Power-up.
Turtle Tantrum! (5) Destroy more than 5 enemies using a destructible object.
Slow as a Turtle (10) Complete a level in under 3 minutes.
Lean, Green and Mean (20) Achieve more than 8,000 points.
Toe Be or Not Toe Be? (20) Avoid all traps in Level 3.
Ice, Ice, Turtle (20) Avoid Ice Ray traps in Level 8.
Staying Alive (25) Defeat the Final Boss without dying.
Turtle Power (25) Complete the game in Story Mode. (Normal difficulty onwards).
I Will Survive (30) Complete a Survival Mode game. (Normal difficulty onwards)
Heroes in a Half Shell (30) Complete the game with all 4 Turtles.
Unlock Levels for Quickplay Mode

Play story mode and defeat the boss at the end of a level to unlock that stage in quickplay mode.

TMNT Re-shelled Glitches

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Keep your score after losing all of your lives in single player story mode.

After getting the game over screen, DO NOT CONTINUE. Instead let the game take you back to the main menu and then choose "Continue Game". You'll start at the beginning of the level that you died on, along with the points that you had when you entered the stage. (NOTE: this doesn't work on stage 1)