Here is the full list of all 27 Runt of the Litter achievements.
Come to Eini's aid.
Hatch a gryphon.
Talk your way out of Aerie.
Sneak out of Aerie unseen.
Romance a fledgling.
Romance a thrall.
Learn of Eini's childhood.
Kill a wyrm.
Get a guard to help you without resorting to bribery.
Impress the High Council with your gryphon.
Kill a gryphon.
Kill in pursuit of your goals.
Find a cure for dropfeather.
Steal a wyrm egg.
Steal a wild gryphon egg.
Spy on the wyrm riders.
Receive a token of friendship from a wyrm rider.
Die to protect someone you care about.
Earn the High Council's forgiveness.
Have Nistarii vote in your favor.
Join the ranks of the fledglings.
Convince the High Council to allow thralls to be fledglings.
Become fully trusted by both gryphon keepers and thralls.
Start a thrall colony.
Serve under Nistarii.
Apprentice to Inte.
Apprentice to Vaanret.