Here is the full list of all 13 Skeletal Dance Party achievements.
Invite Gucha to the Party.
Invite Eek to the Party.
Invite Frankie to the Party.
Bring Funnybone to Life.
Invite Sybil to the Party.
Resurrect Bethany as a Skeleton.
Resurrect Bethany as a Wight.
Finish Funnybone's Tutorial.
Complete All Side-Quests.
Begin the Final Level.
Assemble a party of skeletal musicians.
Find another necromancer.
Defeat Clerie, for now...