msem-instigator

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

{1}{G}, {T}, Discard a card: Another target creature you control gets +X/+X until end of turn, where X is 4 minus that creature's power.

Flash
{3}, Exile this card from your graveyard: Draw a card.

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)

When this artifact enters, target creature you control seeks secrets. (Give it that Oath Aura. Fulfill it by attacking with it and two or more other creatures to draw a card.)
Equipped creature gets +2/+1. As long as it has an Oath attached to it, it has menace.
Equip {3}

When Roseblood Hart enters, choose one —
• Destroy target artifact.
• Create a Treasure token.

Instant, sorcery, and enchantment spells you cast cost {1} less to cast.

Prowess
When Rosebud Runner enters, exile the top card of your library. During your next turn, you may play that card from exile.

Trample
When Rosenhulk enters, choose one —
• Create two 0/1 green Plant creature tokens with “{T}: Add {G}.”
• Destroy target artifact or enchantment.
• Rosenhulk fights target creature an opponent controls.

Rosesworn Knight gets +1/+1 as long as it's embattled. (A creature is embattled if it has a counter on it or a permanent you control attached to it.)

This land enters tapped. As it enters, choose a color.
{T}: Add one mana of the chosen color.
{1}, {T}, Sacrifice this land: Target creature seeks secrets. (Give it that Oath Aura. Fulfill it by attacking with it and two or more other creatures to draw a card.)

Create a 1/1 green Saproling creature token for each nonland permanent card in your graveyard.

Rot-Sand Ruins enters tapped unless you control another Desert.
{T}: Add {B} or {G}.

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

{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.)

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.

Rousing Path enters tapped unless you control one or fewer other lands.
{T}: Add {U} or {R}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Rouse 4. (Distribute four +1/+1 counters among permanents you control. If they aren't creatures, tap them and they become 0/0 creatures in addition to their other types.)

({T}: Add {R}.)
Rousing Rubble enters tapped.
Double strike
{2}{R}{R}: Rousing Rubble becomes a creature in addition to its other types until end of turn.

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.)

Gain control of up to two target creatures until end of turn. Untap them. They gain haste until end of turn.
Menagerie — If there are five or more creature types among creatures you control, untap all creatures you control. Until end of turn, they gain “{T}: This creature fights another target creature.”

{T}: Add {C}.
{2}, {T}: Add three mana of any one color.
{3}, {T}: Create a colorless artifact token named Lotus Petal with “{T}, Sacrifice this artifact: Add one mana of any color.”

{T}, Pay 1 life: Add {W} or {B}.
{2}, {T}, Sacrifice Royal Hospital and another permanent: Draw a card. Activate only during your turn.