i'll subset my recommendations to those which havent already been suggested and feel most strongly about
Vulpecula: adds a small, but thematic, heal for aether
Aetheric Guard: it just makes sense to have a reflect shield in aether
Griffon: adds a protective deterrent mechanic for air's mostly low hp creatures
Shadling: continues darkness' the niche of gaining strength from opponent
Imp Spirit: a good implementation of using other creatures abilities
Reverent: one of my all-time favorite card ideas. thematically fantastic.
Fallen Crusader: minor cc and a minor grow-like buff in one ability
Guinea Pig: mutation on a stick = fun
Amorphic Goo: Uses the mechanics mostly in place from supernova- in an unpredictably, but likely helpful, way
Graviton Carrier: Makes one of the previously least used cards in the game relevant and useful
Fae: a new interaction between existing cards and the cost to play cards from hand
Rain: if aoe can do damage, why not heal too?