Drogskol Captain

Flying
Other Spirit creatures you control get +1/+1 and have hexproof. (They can't be the targets of spells or abilities your opponents control.)

Loam Dweller

Whenever you cast a Spirit or Arcane spell, you may put a land card from your hand onto the battlefield tapped.

O-Kagachi, Vengeful Kami

Flying, trample
Whenever O-Kagachi deals combat damage to a player, if that player attacked you during their last turn, exile target nonland permanent that player controls.

Oyobi, Who Split the Heavens

Flying
Whenever you cast a Spirit or Arcane spell, create a 3/3 white Spirit creature token with flying.

Long-Forgotten Gohei

Arcane spells you cast cost {1} less to cast.
Spirit creatures you control get +1/+1.

Vanquisher's Banner

As this artifact enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
Whenever you cast a creature spell of the chosen type, draw a card.

Reflections of Littjara

As this enchantment enters, choose a creature type.
Whenever you cast a spell of the chosen type, copy that spell. (A copy of a permanent spell becomes a token.)

Rattlechains

Flash
Flying
When this creature enters, target Spirit gains hexproof until end of turn.
You may cast Spirit spells as though they had flash.