Dorothea's Retribution

Enchant creature
Enchanted creature has "Whenever this creature attacks, create a 4/4 white Spirit creature token with flying that's tapped and attacking. Sacrifice that token at end of combat."
If Dorothea's Retribution would be put into a graveyard from anywhere, exile it instead.

Dorothea, Vengeful Victim

Flying
When Dorothea, Vengeful Victim attacks or blocks, sacrifice it at end of combat.
Disturb {1}{W}{U} (You may cast this card from your graveyard transformed for its disturb cost.)

Dorothea, Vengeful Victim // Dorothea's Retribution

Worship

If you control a creature, damage that would reduce your life total to less than 1 reduces it to 1 instead.

Curious Obsession

Enchant creature
Enchanted creature gets +1/+1 and has "Whenever this creature deals combat damage to a player, you may draw a card."
At the beginning of your end step, if you didn't attack with a creature this turn, sacrifice Curious Obsession.

Strict Proctor

Flying
Whenever a permanent entering causes a triggered ability to trigger, counter that ability unless its controller pays {2}.

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.)

Island

Empyrean Eagle

Flying
Other creatures you control with flying get +1/+1.

Geistlight Snare

This spell costs {1} less to cast if you control a Spirit. It also costs {1} less to cast if you control an enchantment.
Counter target spell unless its controller pays {3}.

Shacklegeist

Flying
Shacklegeist can block only creatures with flying.
Tap two untapped Spirits you control: Tap target creature you don't control.

Port Town

As Port Town enters, you may reveal a Plains or Island card from your hand. If you don't, Port Town enters tapped.
{T}: Add {W} or {U}.

Moorland Haunt

{T}: Add {C}.
{W}{U}, {T}, Exile a creature card from your graveyard: Create a 1/1 white Spirit creature token with flying.

Remorseful Cleric

Flying
Sacrifice Remorseful Cleric: Exile target player's graveyard.

Prairie Stream

({T}: Add {W} or {U}.)
Prairie Stream enters tapped unless you control two or more basic lands.

Watcher of the Spheres

Flying
Creature spells with flying you cast cost {1} less to cast.
Whenever another creature you control with flying enters, Watcher of the Spheres gets +1/+1 until end of turn.

Plains

Celestial Purge

Nimbus Maze

{T}: Add {C}.
{T}: Add {W}. Activate only if you control an Island.
{T}: Add {U}. Activate only if you control a Plains.

Spectral Sailor

Flash (You may cast this spell any time you could cast an instant.)
Flying
{3}{U}: Draw a card.

Lofty Denial

Counter target spell unless its controller pays {1}. If you control a creature with flying, counter that spell unless its controller pays {4} instead.

Supreme Phantom

Flying
Other Spirits you control get +1/+1.

Declaration in Stone

Exile target creature and all other creatures its controller controls with the same name as that creature. That player investigates for each nontoken creature exiled this way.

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Skybridge Towers

Skybridge Towers enters tapped.
{T}: Add {W} or {U}.
{2}{W}{U}, {T}, Sacrifice Skybridge Towers: Draw a card.

Rattlechains

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