Brinebound Gift

Enchant creature
Whenever Brinebound Gift enters or enchanted creature becomes the target of an Aura spell, create a 1/1 white Spirit creature token with flying.
If Brinebound Gift would be put into a graveyard from anywhere, exile it instead.

Have

Brine Comber

Whenever Brine Comber enters or becomes the target of an Aura spell, create a 1/1 white Spirit creature token with flying.
Disturb {W}{U} (You may cast this card from your graveyard transformed for its disturb cost.)

Brine Comber // Brinebound Gift

Knight of Doves

Whenever an enchantment you control is put into a graveyard from the battlefield, create a 1/1 white Bird creature token with flying.

Bident of Thassa

Whenever a creature you control deals combat damage to a player, you may draw a card.
{1}{U}, {T}: Creatures your opponents control attack this turn if able.

Entity Tracker

Flash
Eerie — Whenever an enchantment you control enters and whenever you fully unlock a Room, draw a card.

Naiad of Hidden Coves

During turns other than yours, spells you cast cost {1} less to cast.

Sejiri Refuge

Sejiri Refuge enters tapped.
When Sejiri Refuge enters, you gain 1 life.
{T}: Add {W} or {U}.

Starlit Mantle

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature you control
When Starlit Mantle enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+1.

Daxos, Blessed by the Sun

Daxos's toughness is equal to your devotion to white. (Each {W} in the mana costs of permanents you control counts toward your devotion to white.)
Whenever another creature you control enters or dies, you gain 1 life.

Mesa Enchantress

Whenever you cast an enchantment spell, you may draw a card.

Whitewater Naiads

Constellation — Whenever Whitewater Naiads or another enchantment you control enters, target creature can't be blocked this turn.

Archon of Sun's Grace

Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)
Pegasus creatures you control have lifelink.
Constellation — Whenever an enchantment you control enters, create a 2/2 white Pegasus creature token with flying.

Light of Promise

Enchant creature
Enchanted creature has "Whenever you gain life, put that many +1/+1 counters on this creature."

Island

Dawnhart Geist

Whenever you cast an enchantment spell, you gain 2 life.

Fae Flight

Flash
Enchant creature
When Fae Flight enters, enchanted creature gains hexproof until end of turn.
Enchanted creature gets +1/+0 and has flying.

Omen of the Sun

Flash
When Omen of the Sun enters, create two 1/1 white Human Soldier creature tokens and you gain 2 life.
{2}{W}, Sacrifice Omen of the Sun: Scry 2.

Sentinel's Mark

Flash
Enchant creature
Enchanted creature gets +1/+2 and has vigilance.
Addendum — When Sentinel's Mark enters, if you cast it during your main phase, enchanted creature gains lifelink until end of turn.

Gremlin Tamer

Eerie — Whenever an enchantment you control enters and whenever you fully unlock a Room, create a 1/1 red Gremlin creature token.

Dovin, Architect of Law

+1: You gain 2 life and draw a card.
−1: Tap target creature. It doesn't untap during its controller's next untap step.
−9: Tap all permanents target opponent controls. That player skips their next untap step.

Cradle of Safety

Flash
Enchant creature you control
When Cradle of Safety enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+1.

Tranquil Cove

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {W} or {U}.

Mentor of the Meek

Whenever another creature you control with power 2 or less enters, you may pay {1}. If you do, draw a card.

Plains

Military Discipline

Flash
Enchant creature
When Military Discipline enters, enchanted creature gains first strike until end of turn.
Enchanted creature gets +1/+0.

Celestial Ancient

Flying
Whenever you cast an enchantment spell, put a +1/+1 counter on each creature you control.

Feather of Flight

Flash
Enchant creature
When Feather of Flight enters, draw a card.
Enchanted creature gets +1/+0 and has flying.

Gleam of Authority

Enchant creature
Enchanted creature gets +1/+1 for each +1/+1 counter on other creatures you control.
Enchanted creature has vigilance and "{W}, {T}: Bolster 1." (To bolster 1, choose a creature with the least toughness among creatures you control and put a +1/+1 counter on it.)

Inquisitive Glimmer

Enchantment spells you cast cost {1} less to cast.
Unlock costs you pay cost {1} less.

Unwilling Vessel

Vigilance
Eerie — Whenever an enchantment you control enters and whenever you fully unlock a Room, put a possession counter on Unwilling Vessel.
When Unwilling Vessel dies, create an X/X blue Spirit creature token with flying, where X is the number of counters on Unwilling Vessel.

Optimistic Scavenger

Eerie — Whenever an enchantment you control enters and whenever you fully unlock a Room, put a +1/+1 counter on target creature.

Impassioned Orator

Whenever another creature you control enters, you gain 1 life.

Shardmage's Rescue

Flash
Enchant creature you control
As long as Shardmage's Rescue entered this turn, enchanted creature has hexproof.
Enchanted creature gets +1/+1.

Ephara, Ever-Sheltering

Ephara, Ever-Sheltering has lifelink and indestructible as long as you control at least three other enchantments.
Whenever another enchantment you control enters, draw a card.

Invasion of Theros

(As a Siege enters, choose an opponent to protect it. You and others can attack it. When it's defeated, exile it, then cast it transformed.)
When Invasion of Theros enters, search your library for an Aura, God, or Demigod card, reveal it, put it into your hand, then shuffle.