Stop a Cerberus kidnapping.

Modify a weapon.

Visit a store in the single-player campaign.

Return to active duty.

Complete Mass Effect 2 twice, or complete it once with a character imported from Mass Effect 1

Use the Omega 4 Relay

Hack a geth collective

Gain the loyalty of the quarian

Fully upgrade a weapon

Help the Justicar resolve her mission

Gain the loyalty of the krogan

Gain the loyalty of the Professor