msem-instigator

Target creature you control gets +2/+2 until end of turn and must be blocked this turn if able.

Rakkiri Initiate gets +0/+2 as long as it's embattled. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

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

Whenever you cast a spell that doesn't share a color with Raloran Adept, you may switch target creature's power and toughness until end of turn.

Target creature you control gets +1/+1 and gains hexproof until end of turn.

Enchant opponent
When Ranidaphobia enters, create a 1/1 blue Frog creature token.
Creatures enchanted player controls can't block Frogs.

Choose a Function added to Rapid Recursion. Create a Function token with those effects. (It's an enchantment. As you cast an instant or sorcery spell, sacrifice any number of Functions to add their effects to that spell.)
Draw a card.

Target creature can't be blocked this turn. It explores. (Reveal the top card of your library. Put it into your hand if it's a land. Otherwise, put a +1/+1 counter on that creature, then you may put that card in your graveyard.)

Menace
When Rattled Bones dies, forebode. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)

Equipped creature is a Flagbearer in addition to its other types.
While an opponent is choosing targets as part of casting a spell they control or activating an ability they control, that player must choose at least one Flagbearer on the battlefield if able.
Equip {5}

First strike, trample
Whenever a creature dealt combat damage by Ravenous Forsaken this turn dies, put a +1/+1 counter on Ravenous Forsaken.
{2}{R}: Ravenous Forsaken gets +3/+0 until end of turn.

Ravenous Hydra enters with X +1/+1 counters on it.
Whenever Ravenous Hydra deals combat damage, proliferate. (You choose any number of permanents and/or players with counters on them, then give each another kind of a counter already there.)

Whenever a Survivor you control enters, you may draw a card. If you do, discard a card.

Once each turn, when a creature you control enters, you may draw a card if its power is greater than each other creature's power.

Enchant creature
Enchanted creature has deathtouch and “When this creature dies, create a 2/2 black Demon creature token.”
{1}{B}, Exile Reaping Mask from your graveyard: Create a 2/2 black Demon creature token.

Haste
Whenever Reckless Dunerider attacks, if it's enchanted or equipped, you may draw a card. If you do, discard a card.

{T}: Target creature gains haste until end of turn.
{1}{R}, {T}, Sacrifice a Human: Create a token that's a copy of the sacrificed creature, except it's a 3/2 colorless Horror. It gains haste until end of turn. Activate only as a sorcery.

Reckless Rage deals 4 damage to target creature you don't control and 2 damage to target creature you control.

Whenever you cast a noncreature spell, you may put a progress counter on Reckless Research.
[progress 2+] At the beginning of your end step, mill two cards.
[progress 7+] At the beginning of your upkeep, choose target instant or sorcery card in your graveyard. You may cast it from your graveyard this turn.
At the beginning of your upkeep, choose target instant or sorcery card in your graveyard. You may cast it from your graveyard this turn.

{2}{B}{B}, Exile Reclusive Augur from your graveyard: Return another target creature card from your graveyard to the battlefield. Activate only during your turn.

When Recollection Revelation enters, rouse 1. (Put a +1/+1 counter on a permanent you control. If it isn't a creature, tap it and it becomes a 0/0 creature in addition to its other types.)
{1}{W}, Sacrifice Recollection Revelation: Return another target artifact or enchantment card from your graveyard to your hand.

Menace
Crew 2 (Tap any number of creatures you control with total power 2 or greater: This Vehicle becomes an artifact creature until end of turn.)

When Recruits of the Demeter enters, draw a card if you control another Pirate.

Redgill Corsair gets +1/+0 as long as you control an artifact.
When Redgill Corsair dies, create a Treasure token.

Whenever you draw a card, put a hatch counter on Reefcrown Egg.
{T}, Sacrifice Reefcrown Egg: You may put a creature card with mana value less than or equal to the number of hatch counters on Reefcrown Egg from your hand onto the battlefield.
Cycling {2} ({2}, Discard this card: Draw a card.)