Have

Skyknight Squire

Whenever another creature you control enters, put a +1/+1 counter on this creature.
As long as this creature has three or more +1/+1 counters on it, it has flying and is a Knight in addition to its other types.

Savannah Lions

Leonin Vanguard

At the beginning of combat on your turn, if you control three or more creatures, this creature gets +1/+1 until end of turn and you gain 1 life.

Regal Caracal

Other Cats you control get +1/+1 and have lifelink. (Damage dealt by those creatures also causes you to gain that much life.)
When this creature enters, create two 1/1 white Cat creature tokens with lifelink.

Sheltered by Ghosts

Enchant creature you control
When Sheltered by Ghosts enters, exile target nonland permanent an opponent controls until Sheltered by Ghosts leaves the battlefield.
Enchanted creature gets +1/+0 and has lifelink and ward {2}.

Surge of Salvation

You and permanents you control gain hexproof until end of turn. Prevent all damage that black and/or red sources would deal to creatures you control this turn.

Plains

Split Up

Choose one —
• Destroy all tapped creatures.
• Destroy all untapped creatures.

Rest in Peace

When Rest in Peace enters, exile all graveyards.
If a card or token would be put into a graveyard from anywhere, exile it instead.

Ajani, Caller of the Pride

+1: Put a +1/+1 counter on up to one target creature.
−3: Target creature gains flying and double strike until end of turn.
−8: Create X 2/2 white Cat creature tokens, where X is your life total.

Felidar Cub

Sacrifice this creature: Destroy target enchantment.

Jazal Goldmane

First strike (This creature deals combat damage before creatures without first strike.)
{3}{W}{W}: Attacking creatures you control get +X/+X until end of turn, where X is the number of attacking creatures.

Arahbo, the First Fang

Other Cats you control get +1/+1.
Whenever Arahbo or another nontoken Cat you control enters, create a 1/1 white Cat creature token.

Elspeth's Smite

Elspeth's Smite deals 3 damage to target attacking or blocking creature. If that creature would die this turn, exile it instead.

Get Lost

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.")

Case of the Gateway Express

When this Case enters, choose target creature you don't control. Each creature you control deals 1 damage to that creature.
To solve — Three or more creatures attacked this turn. (If unsolved, solve at the beginning of your end step.)
Solved — Creatures you control get +1/+0.

Cavern of Souls

As Cavern of Souls enters, choose a creature type.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type, and that spell can't be countered.

Kutzil's Flanker

Flash
When Kutzil's Flanker enters, choose one —
• Put a +1/+1 counter on Kutzil's Flanker for each creature that left the battlefield under your control this turn.
• You gain 2 life and scry 2.
• Exile target player's graveyard.

Helpful Hunter

Soulstone Sanctuary

{T}: Add {C}.
{4}: This land becomes a 3/3 creature with vigilance and all creature types. It's still a land.

Claws Out

This spell costs {1} less to cast for each Cat you control.
Creatures you control get +2/+2 until end of turn.