Drogskol Reinforcements

Melee (Whenever this creature attacks, it gets +1/+1 until end of turn for each opponent you attacked this combat.)
Other Spirits you control have melee.
Prevent all noncombat damage that would be dealt to Spirits you control.

King of the Oathbreakers

Flying
Whenever King of the Oathbreakers or another Spirit you control becomes the target of a spell, it phases out. (Treat it and anything attached to it as though they don't exist until your next turn.)
Whenever King of the Oathbreakers or another Spirit you control phases in, create a tapped 1/1 white Spirit creature token with flying.

Andúril, Flame of the West

Equipped creature gets +3/+1.
Whenever equipped creature attacks, create two tapped 1/1 white Spirit creature tokens with flying. If that creature is legendary, instead create two of those tokens that are tapped and attacking.
Equip {2}

Scapegoat

As an additional cost to cast this spell, sacrifice a creature.
Return any number of target creatures you control to their owner's hand.

Guardian of Faith

Flash
Vigilance
When Guardian of Faith enters, any number of other target creatures you control phase out. (Treat them and anything attached to them as though they don't exist until their controller's next turn.)

Selfless Spirit

Flying
Sacrifice Selfless Spirit: Creatures you control gain indestructible until end of turn.

Séance Board

Morbid — At the beginning of each end step, if a creature died this turn, put a soul counter on Séance Board.
{T}: Add X mana of any one color, where X is the number of soul counters on Séance Board. Spend this mana only to cast instant, sorcery, Demon, and Spirit spells.

Windborn Muse

Flying
Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Horobi, Death's Wail

Flying
Whenever a creature becomes the target of a spell or ability, destroy that creature.

Path to Exile

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Drumbellower

Flying
Untap all creatures you control during each other player's untap step.

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Thalisse, Reverent Medium

At the beginning of each end step, create X 1/1 white Spirit creature tokens with flying, where X is the number of tokens you created this turn.

Katilda's Rising Dawn

Enchant creature
Enchanted creature has flying, lifelink, and protection from Vampires, and it gets +X/+X, where X is the number of permanents you control that are Spirits and/or enchantments.
If Katilda's Rising Dawn would be put into a graveyard from anywhere, exile it instead.

Katilda, Dawnhart Martyr

Flying, lifelink, protection from Vampires
Katilda, Dawnhart Martyr's power and toughness are each equal to the number of permanents you control that are Spirits and/or enchantments.
Disturb {3}{W}{W} (You may cast this card from your graveyard transformed for its disturb cost.)