Here is the full list of all 10 Seeker: My Shadow achievements.
Collect first Seeker egg.
Collect all Seeker eggs.
Collect first Seeker card
Collect all Seeker cards.
Activate co-op mode in any level.
Speak with Viktor.
Speak with Chlaus
Manifest as Spirit
Speak with Crystape
Speak with a Jesterian.