Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Barren (20 points): Destroy all mushrooms on the screen Centipede - Default difficulty.
Entity (20 points): Have 3 lives in hand: Millipede - Default difficulty.
Eradicate (20 points): Reach wave 8 without a millipede reaching the bottom: Millipede - Default difficulty.
Exterminate (20 points): Reach wave 8 without a centipede reaching the bottom: Centipede - Default difficulty.
Lunatic (20 points): Score 25,000 points: Millipede - Throttle Monkey mode.
Maniac (20 points): Score over 15,000: Centipede - Throttle Monkey mode.
Marauder (10 points): Score 125,000 points: Millipede - Default difficulty.
Poison (20 points): Destroy a spider for 1800 points: Millipede - Default difficulty.
Prowler (10 points): Score over 41,916 to get on the high score table: Millipede - Default difficulty.
Slayer (10 points): Score over 16,543 to beat the high score table: Centipede - Default difficulty.
Spirit (20 points): Have 3 lives in hand: Centipede - Default difficulty.
Stalker (10 points): Score over 50,000 points: Centipede - Default difficulty.