Accomplish the indicated achievement to get the 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.