msem-instigator

Haste
Whenever Quinn or another creature you control enters, tap all creatures your opponents control.

Deathtouch
Whenever a creature dealt damage by Rabid Rodent this turn dies, put a +1/+1 counter on Rabid Rodent.
{2}, Remove a +1/+1 counter from Rabid Rodent: Regenerate Rabid Rodent.

When Rabudan Chiseler enters, you may search your library for an Aura or Equipment card, reveal it, put it into your hand, then shuffle.

Whenever an enchantment you control enters, create a 1/1 colorless Construct Actor creature token.
Token creatures you control have vigilance.

Trample
Cadence (Whenever you cast a spell, if its mana value is greater than this creature's power, put a +1/+1 counter on this creature.)
Whenever Rage-Fueled Adventurer attacks, you may have it fight target creature you don't control.

When Raging Restitched enters, you may sacrifice a creature. When you do, Raging Restitched deals damage to target creature or planeswalker equal to the sacrificed creature's power.

When this creature enters, create a Treasure token.

Flash
When Rahstahde Truthseeker enters, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Haste
Whenever you cast a noncreature spell, put a +1/+1 counter on Rahstahde's Firefist. It gains menace until end of turn.

Haste
When Rainy Night Lovers enters, look at the top four cards of your library. You may cast a red instant or sorcery spell with mana value 1 from among them without paying its mana cost. Then put the rest on the bottom of your library in any order.

Trample
Art of war — At the beginning of your end step, if Raiun Bay Admiral dealt damage to an opponent this turn, put a +1/+1 counter on each other creature you control.

Art of war — At the beginning of your end step, if Raiun Bay Scourge dealt damage to an opponent this turn, gain control of target artifact or enchantment until Raiun Bay Scourge leaves the battlefield.

When Rakkiri Aspirant enters, if you control an embattled creature, exile the top card of your library. Until end of turn, you may play that card. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Haste
Whenever a player casts a spell, Rakkiri Dissident deals 1 damage to that player.

When Ralezza's Disciple enters, if you control an enchantment, you gain 3 life.

Each Merfolk and Wizard you control has “Whenever this creature attacks, abound.” (To abound, you may cast a spell that costs less than that creature from your hand without paying its mana cost.)

Whenever Ram Wrangler attacks, until end of turn, gain control of target creature defending player controls with power less than or equal to the number of creatures in Ram Wrangler's pack. Tap it. It's attacking defending player. (Two or more creatures you control with equal power are in a pack.)

Rammanethi Hydroshaper gets +1/+1 as long as you control an Island.
{2}{U}: Target creature blocking or blocked by Rammanethi Hydroshaper gets -1/-0 until end of turn.

Flash
Voracious 2 (As this enters, you may sacrifice up to two artifacts and/or creatures. This creature enters with that many +1/+1 counters on it.)

When Ramzi, Traveling Merchant enters, adjudicate land. (Create a white enchantment Aura token with enchant land and “Sacrifice this token: Untap enchanted land.” attached to target land.)
Whenever an Aura becomes attached to a land you control, create a 1/1 green Antelope creature token.

When this creature enters, for each kind of counter on target permanent, put another counter of that kind on it or remove one from it.

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.

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Infiltrate (Whenever one or more attacking creatures you control aren't blocked, this creature gets +1/+1 until end of turn.)

When Rat King enters, create two 1/1 black Rat creature tokens with “This creature can't block.”
Whenever Rat King or another creature you control dies, each opponent loses 1 life and you gain 1 life.