When Cloister Gargoyle enters the battlefield, venture into the dungeon. (Enter the first room or advance to the next room.) As long as you've completed a dungeon, Cloister Gargoyle gets +3/+0 and has flying.

When Displacer Beast enters the battlefield, venture into the dungeon. (Enter the first room or advance to the next room.) Displacement — {3}{U}: Return Displacer Beast to its owner's hand.

Flying When Eccentric Apprentice enters the battlefield, venture into the dungeon. (Enter the first room or advance to the next room.) At the beginning of combat on your turn, if you've completed a dungeon, up to one target creature becomes a Bird with base power and toughness 1/1 and flying until end of turn.

{T}: Add {G}.

Room abilities of dungeons you own trigger an additional time.

{T}: Add {G}.

Vigilance Whenever Nadaar, Selfless Paladin enters the battlefield or attacks, venture into the dungeon. (Enter the first room or advance to the next room.) Other creatures you control get +1/+1 as long as you've completed a dungeon.

Reach, ward {1} Whenever you cast a creature or planeswalker spell, venture into the dungeon. This ability triggers only once each turn. (To venture into the dungeon, enter the first room or advance to the next room.) Whenever you complete a dungeon, create a 2/2 green Wolf creature token.

Counter target spell unless its controller pays {1}. Cycling {U} ({U}, Discard this card: Draw a card.)

Choose one — • Counter target spell with mana value 2 or less. • Counter target red or green spell with mana value 6 or less.

This spell can't be countered. Counter target noncreature spell.

Destroy target creature, enchantment, or planeswalker. Its controller creates two Map tokens. (They're artifacts with "{1}, {T}, Sacrifice this artifact: Target creature you control explores. Activate only as a sorcery.")

({T}: Add {G}.)

Glacial Fortress enters the battlefield tapped unless you control a Plains or an Island. {T}: Add {W} or {U}.

Hinterland Harbor enters the battlefield tapped unless you control a Forest or an Island. {T}: Add {G} or {U}.

({T}: Add {U}.)

Overgrown Farmland enters the battlefield tapped unless you control two or more other lands. {T}: Add {G} or {W}.

({T}: Add {W}.)

Companion — Your starting deck contains at least twenty cards more than the minimum deck size. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.) Flying When Yorion enters the battlefield, exile any number of other nonland permanents you own and control. Return those cards to the battlefield at the beginning of the next end step.