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

Castle Reclaimed (10 points): Defeated the guardian of the clocktower.
Dungeon Perfectionist (20 points): Completed all of the dungeon levels.
Boiler Room Perfectionist (20 points): Completed all of the boiler room levels.
Ninja (10 points): Completed "In One Way..." in less than 16 seconds.
Face The Fear (10 points): Completed "Spike Dodging" without using the teleporter.
Abridged (10 points): Completed "Extending Platform" without using the rope.
Shmu Herder (10 points): Completed a level containing Shmu.
Master Of Time (10 points): Completed a time travel level.
Teamwork (40 points): Completed all the CoOp levels.
Gallery Perfectionist (20 points): Completed all of the gallery levels.
Graveyard Perfectionist (20 points): Completed all of the graveyard levels.
Clock Tower Perfectionist (20 points): Completed all of the clocktower levels.