Acid Hydra enters the battlefield with X +1/+1 counters on it.
Drop — When Acid Hydra enters the battlefield, search your library for a creature card with mana value X or less, put it onto the battlefield, then shuffle. Then return that creature to your hand unless you didn't cast any creature spells during your last turn.

Flash
When Agent of Deception enters the battlefield, counter target creature or planeswalker spell unless its controller pays {X}, where X is your devotion to blue.

When All the Stars are Mine enters the battlefield and at the beginning of your upkeep, untap all noncreature permanents you don't control. You gain control of them until end of turn.

When Alluring Queenpin enters the battlefield, create a 3/3 green Elemental Spirit creature token.
Elementals you control get +1/+1.

Flying
When Alrantan Skywatch enters the battlefield, create a 1/1 white Human creature token and draw a card.

When Alrantan Visionary enters the battlefield, reveal the top three cards of your library. Put a noncreature permanent card from among them into your hand and the rest into your graveyard.
{T}: Add one mana of any color.
Wander {4}{G}{G}

When An Unlikely Peace enters the battlefield, mill two cards.
{1}{G}: Return up to two target land cards from your graveyard to your hand.

Flying, menace
When Archon of Condemnation enters the battlefield, you may bless target creature.
At the beginning of your upkeep, you may sacrifice a creature. If you do, bless target creature.

When Arduous Miners enters the battlefield, you may have all players discard a card.
Whenever one or more cards leave your graveyard, create a tapped Treasure token.

Menace
When Arrogant Cabalist enters the battlefield, if you control another Noble, each opponent loses 3 life and you gain 3 life.

When Askir's Rearguard enters the battlefield, if a creature you control dealt combat damage to a player this turn, draw a card.
Wander {1}{U}

When Attuned District enters the battlefield, scry 2.
Whenever you scry, you may pay {1}. If you do, create a 0/0 colorless Construct artifact creature token, then put X +1/+1 counters on it, where X is the number of cards you looked at.

When Avatar of Brilliance enters the battlefield, you may cast target instant or sorcery card in your graveyard with mana value X or less without paying its mana cost, where X is the number of differently named lands you control. If that spell would be put into your graveyard this turn, exile it instead.

When Bangtan Security enters the battlefield, target creature gets +2/+0 and gains indestructible until end of turn.

When Banish to the Isle enters the battlefield, exile up to one target nonland permanent you don't control until Banish to the Isle leaves the battlefield. You gain 3 life.

Barreling Bull can't be blocked by creatures with power 2 or less.
When Barreling Bull enters the battlefield, return a creature you control to its owner's hand.

When Beastbond Instructor enters the battlefield, put a trample counter on target creature you control.

Reach, haste
Drop — When Beat Devastator enters the battlefield, if you didn't cast any creature spells during your last turn, Beat Devastator gains vigilance until end of turn. Up to one target creature blocks it this turn if able.

Trample
When Belligerent Peluda enters the battlefield, it deals 2 damage to any target.

Flash
When Benthalos of Land and Sea enters the battlefield, you may pay {X}. When you do, create a token that's a copy of target white or blue enchantment you control with mana value X or less.

Flash
Multitude {3}{W}{W}
Flying
When Binding Whisper enters the battlefield, tap target creature you don't control.

When Bladeforge Instructor enters the battlefield, put a first strike counter on target creature you control.

When Blasphemous Bonecaller enters the battlefield or dies, you draw a card and you lose 1 life.
{1}{B}, Discard Blasphemous Bonecaller: You draw a card and you lose 1 life.

When Bleakheart Instructor enters the battlefield, put a lifelink counter on target creature you control.

Flash
When Blightfang Zyxthax enters the battlefield, discard a card. If you do, it gains deathtouch until end of turn.