Acidic Slime

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
When Acidic Slime enters, destroy target artifact, enchantment, or land.

Rhythm of the Wild

Creature spells you control can't be countered.
Nontoken creatures you control have riot. (They enter with your choice of a +1/+1 counter or haste.)

Solemn Simulacrum

When Solemn Simulacrum enters, you may search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.
When Solemn Simulacrum dies, you may draw a card.

Nikya of the Old Ways

You can't cast noncreature spells.
Whenever you tap a land for mana, add one mana of any type that land produced.

Tireless Tracker

Landfall — Whenever a land you control enters, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")
Whenever you sacrifice a Clue, put a +1/+1 counter on Tireless Tracker.

Masked Vandal

Changeling (This card is every creature type.)
When Masked Vandal enters, you may exile a creature card from your graveyard. If you do, exile target artifact or enchantment an opponent controls.

Kogla, the Titan Ape

When Kogla, the Titan Ape enters, it fights up to one target creature you don't control.
Whenever Kogla attacks, destroy target artifact or enchantment defending player controls.
{1}{G}: Return target Human you control to its owner's hand. Kogla gains indestructible until end of turn.

Garruk's Packleader

Whenever another creature you control with power 3 or greater enters, you may draw a card.

Kogla and Yidaro

When Kogla and Yidaro enters, choose one —
• It gains trample and haste until end of turn.
• It fights target creature you don't control.
{2}{R}{G}, Discard Kogla and Yidaro: Destroy up to one target artifact or enchantment. Shuffle Kogla and Yidaro into your library from your graveyard, then draw a card.

Toski, Bearer of Secrets

This spell can't be countered.
Indestructible
Toski, Bearer of Secrets attacks each combat if able.
Whenever a creature you control deals combat damage to a player, draw a card.

Brash Taunter

Indestructible
Whenever Brash Taunter is dealt damage, it deals that much damage to target opponent.
{2}{R}, {T}: Brash Taunter fights another target creature.

Elvish Visionary

When Elvish Visionary enters, draw a card.

Beast Whisperer

Whenever you cast a creature spell, draw a card.

Nullstone Gargoyle

Flying
Whenever the first noncreature spell of a turn is cast, counter that spell.

Soul of the Harvest

Trample
Whenever another nontoken creature you control enters, you may draw a card.

Green Slime

Flash
When Green Slime enters, counter target activated or triggered ability from an artifact or enchantment source. If a permanent's ability is countered this way, destroy that permanent.
Foretell {G} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Brown Ouphe

{1}{G}, {T}: Counter target activated ability from an artifact source. (Mana abilities can't be targeted.)

Selvala, Heart of the Wilds

Whenever another creature enters, its controller may draw a card if its power is greater than each other creature's power.
{G}, {T}: Add X mana in any combination of colors, where X is the greatest power among creatures you control.

Haywire Mite

When Haywire Mite dies, you gain 2 life.
{G}, Sacrifice Haywire Mite: Exile target noncreature artifact or noncreature enchantment.

Runic Armasaur

Whenever an opponent activates an ability of a creature or land that isn't a mana ability, you may draw a card.

Ouphe Vandals

{G}, Sacrifice Ouphe Vandals: Counter target activated ability from an artifact source and destroy that artifact if it's on the battlefield. (Mana abilities can't be targeted.)

Cankerbloom

{1}, Sacrifice Cankerbloom: Choose one —
• Destroy target artifact.
• Destroy target enchantment.
• Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Ohran Frostfang

Attacking creatures you control have deathtouch.
Whenever a creature you control deals combat damage to a player, draw a card.