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

Geared Up (5 points): Equip a full suit of armor: helmet, armor and weapon.
Dungeon Delver (5 points): Destroy all monsters in a dungeon level.
Chain Master (10 points): Achieve a 10 kill chain.
Morph to Kill (5 points): Defeat 10 monsters while in Alter Ego form.
Team Work (10 points): Complete 2 quests in one continuous co-op session.
Class Act (10 points): Complete at least one quest with each character.
Master Bomber (10 points): Kill 100 monsters using exploding vases.
God's Champion (20 points): Reach level 20 with any character.
Gold Miser (25 points): Accumulate 500,000 gold.
Treasure Hunter (25 points): Find 15 secret rooms.
Merchant's Master (25 points): Buy or sell 100 items.
Snake Slayer (50 points): Finish the game by defeating the Gorgon.