Whenever an enchantment you control enters, each opponent mills two cards.

Whenever an enchantment you control enters, tap target noncreature permanent.

During your turn, you may play cards from your graveyard but not from anywhere else.
Whenever you cast an instant or sorcery spell, exile that card instead of putting it into your graveyard as it resolves.
If another permanent you control would be put into your graveyard, exile it instead.

Whenever you cast an instant or sorcery spell from your hand, cache it instead of putting it into your graveyard as it resolves.

Level up {1}{R}
[level 1-2] Whenever this creature deals combat damage to a player, target Subroutine you control runs.
[level 3+] Whenever this creature deals combat damage to a player, target Subroutine you control runs twice.

Whenever you cast a multicolored spell, this creature deals 1 damage to each opponent and you gain 1 life.
When this creature dies, create a Treasure token.

Flash
When Omen of Deception enters, counter target spell unless its controller pays {2}.
{2}{U}, Sacrifice Omen of Deception: Scry 2.

Flash
When Omen of Horizons enters, put two +1/+1 counters on target creature you control.
{2}{G}, Sacrifice Omen of Horizons: Scry 2.

Flash
When Omen of Slaughter enters, each opponent sacrifices a creature or planeswalker.
{2}{B}, Sacrifice Omen of Slaughter: Scry 2.

Flash
When Omen of Storms enters, discard a card, then draw two cards.
{2}{R}, Sacrifice Omen of Storms: Scry 2.

Flash
When Omen of Victory enters, create a 0/0 white Army creature token, then put two +1/+1 counters on it.
{2}{W}, Sacrifice Omen of Victory: Scry 2.

Ominous Quag enters tapped.
{T}: Add {W} or {B}.
{2}{W}{B}, {T}, Sacrifice Ominous Quag: Draw a card.

Whenever you draw a card, put a foreshadow counter on this enchantment.
Remove eight foreshadow counters from this enchantment: Create an 8/8 blue Kraken creature token.
Cycling {2}

Whenever Omnoid Destroyer or another artifact you control enters, artifact creatures you control gain deathtouch until end of turn.

Damned — When this creature enters, if you've sacrificed a permanent this turn, create a Treasure token.

Whenever Opal-Eye Allseer enters or you cast a noncreature spell, create a 1/1 white Bird creature token with flying.
Wander—{1}{U}, Exile two instant and/or sorcery cards from your graveyard.

When Opal-Eye Caretaker enters, put a +1/+1 counter on each creature you control that entered this turn and wasn't cast from your hand.
Wander {1}{W}

Flying, haste
As an additional cost to cast spells with flashback, you may pay {1}{R}. When you do, return Opal-Eye Phoenix from your graveyard to the battlefield.

Whenever you spend at least five mana to cast a spell, untap Opal-Eye Runeweaver.
{T}: Untap another target permanent not named Opal-Eye Runeweaver. Activate only as a sorcery.

Open Air Boardwalk enters tapped.
{T}: Add {G} or {W}.
{4}: Make a pledge. Activate only as a sorcery.

When Opulent Roughrider enters or leaves the battlefield, surveil 1, then you may reveal the top card of your library. If that card has the same name as a permanent you control or a card in your graveyard, put it into your hand.
Wander {4}{U}{U}

When this land enters, you gain 2 life.
{T}: Add {C}. You may spend this mana as though it were mana of any color to activate cycling abilities or cast spells with a cycling ability.

Whenever you cast an instant or sorcery spell, Orbinoid gets +1/+1 and gains trample until end of turn.

Enchant creature
Whenever enchanted creature attacks, put a +1/+1 counter on it. Then if it has three or more +1/+1 counters on it, sacrifice Ordeal of Athreos.
When you sacrifice Ordeal of Athreos, return target creature card from your graveyard to the battlefield.

Enchant creature
Whenever enchanted creature attacks, put a +1/+1 counter on it. Then if it has three or more +1/+1 counters on it, sacrifice Ordeal of Ephara.
When you sacrifice Ordeal of Ephara, return up to two target nonland permanents to their owner's hand.