Covertly kill 25 unaware enemies

Use a trip mine to kill an enemy who is trying to assault your position

Purchase all skills in all categories.

Complete all optional tombs.

Find 75% of all documents.

Collect 75% of all relics.

Complete one challenge.

Kill 75 enemies with the rifle.

Kill 50 enemies with the bow.

Kill 25 unaware enemies.

Collect 5000 pieces of salvage.

Perform 50 headshot kills in the single player campaign.

Collect 25% of all relics.