msem-instigator

{1}{U}, {T}, Discard a card: Reveal the top card of your library. Counter target spell unless its controller pays {X}, where X is the mana value of that card.

{T}, Sacrifice Rootshambler: Untap all basic lands you control.

At the beginning of each upkeep, choose another permanent with the greatest mana value among permanents. Its controller sacrifices it.

When Rotfeeder Slime dies, you gain 2 life for each creature card in your graveyard.

Rotrider Renegade can't block or be blocked.
{1}{B}: Rotrider Renegade gets +1/+1 until end of turn.
Dash—Reveal a Rogue card from your hand, Pay 2 life (You may cast this spell for its dash cost. If you do, it gains haste, and it's returned from the battlefield to its owner's hand at the beginning of the next end step.)

{2}{G}: Rotted Kalak gains indestructible until end of turn.
Revive {3}{B} ({3}{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.)

Deathtouch

When Rotting Greatwurm dies, put three +1/+1 counters on target creature you control.
Fleeting {2}{G} (You may cast this spell for its fleeting cost. If you do, sacrifice it at the beginning of the next end step.)

{T}: Add {B} or {G}. You lose 1 life.

{1}{B}, Exile a creature or land card from your graveyard: Return Rotwood Whisper from your graveyard to the battlefield tapped.

Once each turn, when Rova, the Fleshweaver enters or you attack with one or more Horrors, you may put a +1/+1 counter on each creature you control. Then if Rova isn't a token, untap each land you control. Until your next turn, you may cast permanent spells as though they had flash.
{2}{G}{G}, Discard Rova: Create a token that's a copy of Rova, the Fleshweaver, except it's 4/4 and isn't legendary. Activate only as a sorcery.

Whenever Roving Dreadnought attacks, you may salvage a card that was put into your graveyard this turn. (Exile one from your graveyard until this creature leaves the battlefield. Whenever this creature deals combat damage to a player, put a card it salvaged into your hand.)

First strike
Prevent all noncombat damage that would be dealt to Royal Knight.

When Royal Retriever enters or when a creature you control scavenges it, you may discard a card. If you do, draw a card.
Scavenge {R} ({R}, Exile this card from your graveyard: Put a number of +1/+1 counters equal to this card's power on target creature. Scavenge only as a sorcery.)

When Rubble Seer enters, you may sacrifice a land or exile a land card from your graveyard. If you do, exile the top card of your library. Until the end of your next turn, you may play that card.

Trample
Whenever a noncreature permanent is put into a graveyard from the battlefield, put a +1/+1 counter on Ruinous Naga.

Ruins Monitor can't be blocked by more than one creature.

Trample
Players can't activate abilities of nonbasic, noncreature permanents.

When Ruler of Cities enters, you may search your library for an Aura that could enchant a land you control, reveal it, put it into your hand, then shuffle.
Whenever an Aura becomes attached to a land you control, you gain 2 life.

When Rum Guzzler enters, forebode, then you lose 1 life. (Create a tapped colorless Omen artifact token with “{T}, Discard a card, Sacrifice this artifact: Draw a card.”)

You may spend mana as though it were mana of any color to cast spells with mana value 5 or greater or to activate abilities of permanents or permanent cards with mana value 5 or greater.
{T}: Add {C}.

When Runed Servitor dies, each player draws a card.

Improve {1}{U} ({1}{U}: Put a +1/+1 counter on this creature. This costs {1} more to activate for each +1/+1 counter on it. Improve only as a sorcery.)
At the beginning of your end step, if one or more embattled creatures you controlled dealt damage to a player, you may draw a card. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Whenever you cast a spell that's red, green, white, or blue, each opponent loses 1 life and you gain 1 life.