When Oath of Liliana enters, each opponent sacrifices a creature.

At the beginning of each end step, if a planeswalker entered the battlefield under your control this turn, create a 2/2 black Zombie creature token.

At the beginning of each player's upkeep, that player chooses target player who has more life than they do and is their opponent. The first player may have Oath of Mages deal 1 damage to the second player.

At the beginning of each player's upkeep, that player chooses target player who has more cards in hand than they do and is their opponent. The first player may discard their hand and draw three cards.

Whenever Oath of the Ancient Wood or another enchantment you control enters, you may put a +1/+1 counter on target creature.

Equipped creature gets +3/+1.

Whenever equipped creature dies, return that card to the battlefield under your control if it's a Samurai card.

When Oathkeeper, Takeno's Daisho is put into a graveyard from the battlefield, exile equipped creature.

Equip

Oathsworn Knight enters with four +1/+1 counters on it.

Oathsworn Knight attacks each combat if able.

If damage would be dealt to Oathsworn Knight while it has a +1/+1 counter on it, prevent that damage and remove a +1/+1 counter from it.

+2: Each opponent loses 1 life. You gain life equal to the life lost this way.

−2: Create a 5/5 black Demon creature token with flying. You lose 2 life.

−8: You get an emblem with ", Sacrifice a creature: You gain X life and draw X cards, where X is the sacrificed creature's power."

Ob Nixilis of the Black Oath can be your commander.

Flying, trample

Whenever one or more opponents each lose exactly 1 life, put a +1/+1 counter on Ob Nixilis, Captive Kingpin. Exile the top card of your library. Until your next end step, you may play that card.

Landfall — Whenever a land you control enters, you may have target player lose 3 life. If you do, put three +1/+1 counters on Ob Nixilis, the Fallen.

Flying, trample

Whenever an opponent searches their library, that player sacrifices a creature and loses 10 life.

Whenever another creature dies, put a +1/+1 counter on Ob Nixilis, Unshackled.

: The player whose turn it is may end the turn. (Exile all spells and abilities from the stack. The player whose turn it is discards down to their maximum hand size. Damage wears off, and "this turn" and "until end of turn" effects end.)

, : You gain 5 life.

, : Draw a card, then discard a card.

, : Target creature gets -2/-2 until end of turn.

, : Obelisk of Alara deals 3 damage to target player or planeswalker.

, : Target creature gets +4/+4 until end of turn.

: Add , , or .

: Add , , or .

, : Return target permanent you both own and control to your hand.

Reach

Whenever Obelisk Spider deals combat damage to a creature, put a -1/-1 counter on that creature.

Whenever you put one or more -1/-1 counters on a creature, each opponent loses 1 life and you gain 1 life.

This spell can't be countered.

Destroy all artifacts, creatures, and lands. They can't be regenerated.

Aftermath (Cast this spell only from your graveyard. Then exile it.)

Target opponent discards two cards.

When Oblivion Ring enters, exile another target nonland permanent.

When Oblivion Ring leaves the battlefield, return the exiled card to the battlefield under its owner's control.

, : Put a fate counter on target permanent.

, , Sacrifice Oblivion Stone: Destroy each nonland permanent without a fate counter on it, then remove all fate counters from all permanents.

Target creature you control gains indestructible until end of turn. Draw a card if that creature has a +1/+1 counter on it. (Damage and effects that say "destroy" don't destroy the creature.)

Flying

, Return a land you control to its owner's hand: Untap target land.

: Add .

: Return Oboro, Palace in the Clouds to its owner's hand.

Whenever you cast a spell, if its mana value is equal to 1 plus the number of soul counters on Obscura Ascendancy, put a soul counter on Obscura Ascendancy, then create a 2/2 white Spirit creature token with flying.

As long as there are five or more soul counters on Obscura Ascendancy, Spirits you control get +3/+3.

Choose three. You may choose the same mode more than once.

• Until end of turn, target creature loses all abilities and has base power and toughness 1/1.

• Target creature connives. (Draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on that creature.)

• Target player returns a creature card from their graveyard to their hand.

Flash

Lifelink

When Obscura Interceptor enters, it connives. When it connives this way, return up to one target spell to its owner's hand. (To have a creature connive, draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on that creature.)

When Obscura Storefront enters, sacrifice it. When you do, search your library for a basic Plains, Island, or Swamp card, put it onto the battlefield tapped, then shuffle and you gain 1 life.

If you control a commander, you may cast this spell without paying its mana cost.

Prevent all damage that would be dealt this turn by creatures your opponents control.

If it's neither day nor night, it becomes day as Obsessive Astronomer enters.

Whenever day becomes night or night becomes day, discard up to two cards, then draw that many cards.

Draw a card.

Madness (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

: Draw a card, then discard a card.

, , Sacrifice Obsessive Stitcher: Return target creature card from your graveyard to the battlefield.

Equipped creature gets +2/+1 and has haste.

Whenever a Warrior creature enters, you may attach Obsidian Battle-Axe to it.

Equip

: Put a blaze counter on target land without a blaze counter on it. For as long as that land has a blaze counter on it, it has "At the beginning of your upkeep, this land deals 1 damage to you." (The land continues to burn after Obsidian Fireheart has left the battlefield.)

When Obstinate Baloth enters, you gain 4 life.

If a spell or ability an opponent controls causes you to discard Obstinate Baloth, put it onto the battlefield instead of putting it into your graveyard.

Obstinate Gargoyle has flying as long as it's modified. (Equipment, Auras you control, and counters are modifications.)

Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Flash

Flying

Whenever another Faerie you control enters, each opponent loses 1 life.

When Obzedat, Ghost Council enters, target opponent loses 2 life and you gain 2 life.

At the beginning of your end step, you may exile Obzedat. If you do, return it to the battlefield under its owner's control at the beginning of your next upkeep. It gains haste.

Draw X cards, then discard X cards. Create a 1/1 white Spirit creature token with flying for each card type among cards discarded this way.

First strike, lifelink

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)

At the beginning of your end step, if you gained life this turn, create a 1/1 white Cat creature token. Then if you have the city's blessing, for each token you control that entered this turn, create a token that's a copy of it.

Trample

Ochre Jelly enters with X +1/+1 counters on it.

Split — When Ochre Jelly dies, if it had two or more +1/+1 counters on it, create a token that's a copy of it at the beginning of the next end step. The token enters with half that many +1/+1 counters on it, rounded down.

When Octo Opus enters, create a 4/4 blue Octopus Performer creature token named Contortionist with "At the beginning of your upkeep, you may fold this token in half." (It becomes 2/2, then 1/1, ½/½, and so on.)

Sacrifice Octo Opus: Draw a card and an additional card for each of Contortionist's folds.

When Octoprophet enters, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Enchant creature

Enchanted creature has ": Draw a card."

: Enchanted creature gains vigilance until end of turn.

Flying

As long as you control a transformed permanent, Oculus Whelp has "When Oculus Whelp dies, draw a card."

At the beginning of each combat, creatures you control gain banding until end of turn if a creature you control has banding. The same is true for changeling, devoid, fear, flanking, horsemanship, ingest, intimidate, landwalk, shroud, tantrum, wither, and the activated ability "Sacrifice this creature: Add ."

: Regenerate Odious Trow.

When Odric, Blood-Cursed enters, create X Blood tokens, where X is the number of abilities from among flying, first strike, double strike, deathtouch, haste, hexproof, indestructible, lifelink, menace, reach, trample, and vigilance found among creatures you control. (Count each ability only once.)

First strike (This creature deals combat damage before creatures without first strike.)

Whenever Odric, Master Tactician and at least three other creatures attack, you choose which creatures block this combat and how those creatures block.

When Odunos River Trawler enters, return target enchantment creature card from your graveyard to your hand.

, Sacrifice Odunos River Trawler: Return target enchantment creature card from your graveyard to your hand.

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)

I — Put a +1/+1 counter on up to one target creature. Create a Food token.

II — Draw a card. Create a Food token.

III — Create a 1/1 white Halfling creature token for each Food you control.