msem-instigator

Whenever Rustshell Mantis is dealt damage, put that many +1/+1 counters on it. (It must survive the damage to get the counters.)

Deathtouch
Whenever Ruststep Centipede deals combat damage to a player, you may destroy target artifact or enchantment that player controls.

First strike
Ruthless Blademaster gets +1/+0 for each Equipment attached to it.

{2}{R}: Ruthless Mastiff gets +3/+0 until end of turn.

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)
Ruthless Predator can't be blocked by more than one creature.

{T}, Sacrifice a creature: Conjure a card named Data-Point into your hand. Activate only as a sorcery. (It's a sorcery that costs {2} with “Draw a card.”)

If a player taps a nonbasic land for mana, that land produces {C} instead of any other type.
Whenever Rylei Wakebreaker attacks, it and another target creature you control each get +1/+0 until end of turn for each attacking creature you control.

Haste
Whenever an embattled creature you control deals combat damage to a player, you may pay {2}{G}. If you do, create a token that's a copy of that creature, except the token isn't legendary if the creature is legendary. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Whenever S-40 Wallbreaker attacks, create a 1/1 colorless Construct artifact creature token.
{X}, Sacrifice X artifacts: S-40 Wallbreaker deals X damage to each opponent.

Equipped creature gets +2/+0 and can't be blocked.
Whenever a Rogue you control attacks, you may pay {1}. If you do, attach Saber of Defiled Rites to it.
Equip {5}

When Sabne's Autumn enters, search your library for a Forest card, reveal it, put it into your hand, then shuffle. You gain 3 life.
{1}{G}{G}: Transform Sabne's Autumn. Activate only if your fealty to Forests is five or greater.

Indestructible
Lands you control have “{T}: Add {G}{G}.”
{5}{G}{G}: Double the power and toughness of each creature you control until end of turn.

Spells you cast during combat cost {1} less to cast.
Spells your opponents cast during combat cost {1} more to cast.

Sacred Summits enters tapped.
{T}: Add one mana of any color among the color identity of legendary creatures and planeswalkers you control or legendary cards in your command zone.

{G}: Exile target card from a graveyard. If it was a land card, put a +1/+1 counter on Sacrificial Bull.
{G}, Sacrifice Sacrificial Bull: You gain life equal to its power.

Trample
When Saddlesaur Guide enters, create a green Aura enchantment token named Hefty Load attached to target creature. The token has enchant creature and “Enchanted creature gets +2/+2 and has trample.”

Reach
{T}: Sadistic Sparkmage deals 1 damage to each opponent.

Return target creature or land card from your graveyard to your hand. You may shuffle up to three cards from your graveyard into your library.

Whenever a creature in Sage of Circular Motion's pack becomes the target of a spell, draw a card. (Two or more creatures you control with equal power are in a pack.)

Whenever Sage of Reflections attacks, mill three cards, then choose a creature card milled this way. Create a token that's a copy of it that's tapped and attacking, except it has no mana cost.

Reach
When Sage of Staves enters, choose one —
• Sage of Staves deals 3 damage to target player or planeswalker.
• Put a +1/+1 counter on target creature you control.

Sage's Ashes enters tapped.
{T}, Sacrifice Sage's Ashes: Put target card from a graveyard on top of its owner's library.
{3}, Exile Sage's Ashes from your graveyard: Draw a card.

Whenever a land creature you control deals combat damage to a player, put a +1/+1 counter on it.
{1}{G}: Put a +1/+1 counter on target land you control. It becomes a 0/0 Elemental creature that's still a land.

Trample
Whenever Saghira, Divinity's Usurper attacks, you may pay {1}{G}. If you do, destroy target artifact, enchantment, or creature with flying.

Vigilance
{1}{G}{G}: Sahalia Dragoons gets +4/+4 until end of turn. Activate only once each turn.