msem-instigator

Sacrifice a creature: Rapacious Demon gets +1/+1 and gains flying until end of turn. Activate only as a sorcery.

Haste
Whenever Rapid Rodent attacks, it gets +1/+0 until end of turn for each other creature you control with flash and/or haste.

Reach, deathtouch
Whenever you cast a spell from your graveyard, you may have Raven-Cursed Dominik fight target creature.

Whenever one or more other creatures you control deal combat damage to an opponent, choose one —
• That player discards a card at random.
• That player sacrifices a creature with toughness 4 or less.

When Ravenous Chupacabra enters, destroy target creature an opponent controls.

Double strike

When Raving Brigand enters, forebode. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)
Whenever you sacrifice an Omen, target player mills three cards.

Flying
Whenever an opponent discards one or more cards, fateseal 1. (To fateseal 1, look at the top card of an opponent's library, then you may put it on the bottom of that player's library.)

Whenever another creature you control dies, target player loses 1 life and you gain 1 life.
{1}{B}, Sacrifice a creature: Scry 1. (To scry 1, look at the top card of your library. You may put that card on the bottom of your library.)

When Realmwalker Domovoi enters, exile another target permanent you control. Return it to the battlefield under your control at the beginning of the next end step.

Whenever a Plains you control enters, you may put a creature card with mana value 2 or less from your hand onto the battlefield.

This creature gets +1/+1 for each creature card in your graveyard.
{4}{R}, Sacrifice another creature: Gain control of target creature until end of turn. Untap that creature. It gains haste until end of turn. Activate only as a sorcery.

Rhapsody {4}{R}{R} (Pay {4}{R}{R} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
When Reckless Guardian dies, create X 1/1 colorless Servo artifact creature tokens, where X is Reckless Guardian's power.

Haste
Whenever Reckless Pyremage becomes tapped, it deals 1 damage to each creature and each player.

When Reclamation Sage enters, you may destroy target artifact or enchantment.

When Recon Drone enters, you may search your library for a basic land card, reveal it, put it into your hand, then shuffle. Then if you did, put a card from your hand on the bottom of your library.

When Red Flower Assassin enters, destroy target creature.
Revive {5}{B} ({5}{B}, Exile this card from your graveyard: Create a token that's a copy of it except it has no mana cost. Revive only as a sorcery.)

When Red-Crowned Admiral enters, create an Idol token. (It's an artifact with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)
Each creature you control with a +1/+1 counter on it has flying.

Other creatures you control get +0/+1.
{T}: Add {G}.

Redleather Armorer gets +1/+1 as long as it's your turn.

First strike
Whenever an opponent casts a noncreature spell, you gain 2 life.

As Reflective Stalker enters, choose a noncreature card name.
When Reflective Stalker enters, if it was cast, create a token that's a copy of it.
Spells your opponents cast with the chosen name cost {2} more to cast.

Flying, lifelink

Menace
Regal Dragoon gets +1/+1 as long as you control a legendary creature.