Bye, Felicia! is unlocked after you have completed the 'Divine Retribution' mission. This mission is the last main story mission (23rd)
After finishing a mission called 'In The Shadow Of Starlight' you will receive the 'Divine Retribution' quest from Lilith
This mission has 11 objectives consisting of:
1. Enter Portal
2. Find Tyreen
3. Defeat Tyreen the Destroyer
4. Collect Vault Key
5. Loot Vault
6. Leave Vault
7. Return to Sanctuary
8. Go to Lilith’s room
9. Give Vault Key to Tannis
10. Talk to Tannis
11. Place Eridian artefact
After placing the artefact you should unlock the achievement along with the story campaign.
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