Defeat an old adversary.

Send a warning across the galaxy.

Reach level 20 in multiplayer or level 60 in single-player.

Attain the highest level of readiness in each theater of war.

Kill 10 guardians with headshots from the front while their shields are raised.

Call down an orbital strike.

Kill 1,000 enemies.

Reach level 15 in multiplayer or level 50 in single-player.

Establish or rekindle a romantic relationship.

Discover an enemy's monstrous origin.

Evolve any of your powers to rank 6.

Survive the swarm.

Defeat a Harvester.