Midnight Guard

Whenever another creature enters, untap this creature.

Numot, the Devastator

Flying
Whenever Numot deals combat damage to a player, you may pay {2}{R}. If you do, destroy up to two target lands.

Pestermite

Flash
Flying
When this creature enters, you may tap or untap target permanent.

Sky Hussar

Flying
When this creature enters, untap all creatures you control.
Forecast — Tap two untapped white and/or blue creatures you control, Reveal this card from your hand: Draw a card. (Activate only during your upkeep and only once each turn.)

Deceiver Exarch

Flash (You may cast this spell any time you could cast an instant.)
When this creature enters, choose one —
• Untap target permanent you control.
• Tap target permanent an opponent controls.

Soul Warden

Whenever another creature enters, you gain 1 life.

Felidar Guardian

When this creature enters, you may exile another target permanent you control, then return that card to the battlefield under its owner's control.

Zealous Conscripts

Haste
When this creature enters, gain control of target permanent until end of turn. Untap that permanent. It gains haste until end of turn.

Timestream Navigator

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
{2}{U}{U}, {T}, Put this creature on the bottom of its owner's library: Take an extra turn after this one. Activate only if you have the city's blessing.

Runaway Steam-Kin

Whenever you cast a red spell, if this creature has fewer than three +1/+1 counters on it, put a +1/+1 counter on this creature.
Remove three +1/+1 counters from this creature: Add {R}{R}{R}.

Impact Tremors

Whenever a creature you control enters, this enchantment deals 1 damage to each opponent.

Restoration Angel

Flash
Flying
When this creature enters, you may exile target non-Angel creature you control, then return that card to the battlefield under your control.

Splinter Twin

Enchant creature
Enchanted creature has "{T}: Create a token that's a copy of this creature, except it has haste. Exile that token at the beginning of the next end step."

Grinning Ignus

{R}, Return this creature to its owner's hand: Add {C}{C}{R}. Activate only as a sorcery.

Soul's Attendant

Whenever another creature enters, you may gain 1 life.

Altar of the Brood

Whenever another permanent you control enters, each opponent mills a card.

Kiki-Jiki, Mirror Breaker

Haste
{T}: Create a token that's a copy of target nonlegendary creature you control, except it has haste. Sacrifice it at the beginning of the next end step.

Ajani's Welcome

Whenever a creature you control enters, you gain 1 life.

Purphoros, God of the Forge

Indestructible
As long as your devotion to red is less than five, Purphoros isn't a creature.
Whenever another creature you control enters, Purphoros deals 2 damage to each opponent.
{2}{R}: Creatures you control get +1/+0 until end of turn.