msem-instigator

Flying, trample
Whenever Raidragos' Avenger deals combat damage to a player, create a 5/5 red Dragon creature token with flying.
Creatures you control get +1/+0 for each Dragon you control.

When Raikai Seafarer enters, you may search your library for up to three cards named Raikai Seafarer, reveal them, put them into your hand, then shuffle.

Menace
When Rallios Unleashed enters, create a 2/2 black Zombie creature token.
Whenever Rallios Unleashed deals combat damage to a player, create a 2/2 black Zombie creature token for each creature card in your graveyard.

When Rampaging Xiangshe 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 trample.

Whenever Ravaging Tyrant enters or attacks, each opponent loses 3 life, discards a card, and sacrifices a creature or planeswalker.

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

Flying

Draw two cards. You may play an additional land this turn.
Coalesce {5}{G}{U} (You may cast this from your graveyard for {5}{G}{U}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

{T}, Sacrifice a land: Untap up to three target lands.

Trial 6 (As you cast this spell, an opponent of your choice may pay 6 life. If they don't, they fail the trial.)
Flying
When Reckoner of Man enters, if the trial was failed, it deals 3 damage to each creature you don't control.

Return up to three target land cards from your graveyard to your hand.
Coalesce {6}{G} (You may cast this from your graveyard for {6}{G}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

Whenever Reclamation Grovesculptor enters or attacks, put a growth counter on target noncreature permanent. It becomes a colorless Forest land and loses all other card types and land types.

Indestructible
When Reflected Worldwalker enters, each player puts their hand into their sideboard.

Instant and sorcery spells you cast cost {1} less to cast.
Whenever you cast an instant or sorcery spell, Regrets of Mortals gets +2/+0 until end of turn. You may discard a card. If you do, draw a card.

Deploy 3 (As this enters, you may tap any number of other creatures you control with total power 3 or more.)
When Relief Battalion enters deployed, draw a card.

Trample
When Remnant of the Wild enters, if you cast it, untap all lands you control.

Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Ward {2}
When Rewriter of Flesh enters, target creature you control becomes an enchantment and loses all other card types. (It still has its abilities, but it's no longer a creature.)

Whenever Rhudai Swathcutter attacks, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Hexproof from mana value 3 or less
{W}: Rhysta of the Roses gains lifelink until end of turn.
{B}: Rhysta of the Roses gains menace until end of turn.

Flying, menace
When Riftkeeper Entity enters, discard your hand, then draw cards equal to the number of differently named lands you control.
{1}{R}, Discard Riftkeeper Entity: Create a tapped colorless land token named Fading Rift with “{T}, Sacrifice this land: Add one mana of any color.”

Flying
Whenever Rimebreath Tyrant attacks, you may discard a card. When you do, tap target creature. It doesn't untap during its controller's next untap step.

This spell can't be countered.
Haste
Whenever a creature dealt damage by Ripper of the Fang Den this turn dies, put X +1/+1 counters on Ripper, where X is his power.