msem-instigator

Deathtouch
Whenever another creature you control dies, each opponent loses 1 life.
{2}{W}: Create a 1/1 colorless Servo artifact creature token.

When you cast Senaturian Centurion, reveal cards from the top of your library until you reveal a creature card with mana value 2 or less. Copy that card, then put the revealed card into your hand. You may cast the copy without paying its mana cost. Put the revealed cards on the bottom of your library in a random order.

When Sending Stones enters, harmonize twice. (To harmonize, trigger up to one harmony of a permanent you control.)
If you would harmonize, you may trigger a harmony of a permanent card in your graveyard instead.

At the beginning of your draw step, draw an additional card and you lose 1 life. Then if you have six or fewer cards in hand, sacrifice a creature.

Death knell — Put a +1/+1, flying, lifelink, or menace counter on Senn, the Haunting Gaze, then trigger a death knell of another permanent you control. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)

When Sensational Festivities enters or at the beginning of your upkeep, you may draw a card. If you do, each opponent may draw a card, then discard a card.

Untap all permanents you control during each other player's untap step.

Soldiercycling {1}{W}, Wizardcycling {1}{U}, Zombiecycling {1}{B}, Warriorcycling {1}{R}, Elfcycling {1}{G} ({1}{G}, Discard this card: Search your library for an Elf card, reveal it, and put it into your hand, then shuffle.)
Sentinel of Latter Days is every creature type as long as it's in your library.

Sentinel of the Highlands has hexproof 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.)

Equipped creature gets +2/+0. As long as it's a Knight, it has first strike.
Equip {1}{W}

Flying, vigilance
Whenever Sepulchral Guide attacks, prevent all combat damage that would be dealt to another target creature you control this turn. If that creature has two or more counters on it, untap it.

Deathtouch, menace
As long as you control another Knight creature, Ser Joffrey, Plague of Nines and other Knight creatures you control have first strike.

Trample
Ser Malcomn's power and toughness are each equal to the number of nonbasic lands your opponents control.

Sera of Coppercove attacks each combat if able.
Whenever Sera of Coppercove attacks, it fights target creature you don't control.
{1}{R}{G}: Sera of Coppercove gets +3/+3 until end of turn.

When Serafina's Gift enters, if you cast it, target opponent gains control of it.
At the beginning of your upkeep, draw three cards, then discard two cards.

Flying, vigilance, lifelink
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Flying
Whenever you cycle Seraph of the Stage or it attacks, audition for white. (Create a 1/1 Construct Actor creature token, a Scout Role giving 2/3 and vigilance, or a Cleric Role giving 2/2 and lifelink. Roles replace older ones.)
Basic landcycling {1}{W} ({1}{W}, Discard this card: Search your library for a basic land card, reveal it, and put it into your hand, then shuffle.)

Serene Chapel enters tapped unless you control a basic Plains.
{T}: Add {W}.
{1}{W}{W}: Until end of turn, Serene Chapel becomes a 2/1 white Spirit Cleric creature with flying and “Whenever this creature attacks, you may exile target card from a graveyard.” It's still a land.

Equipped creature gets +1/+1 and has deathtouch.
{1}: Serpent Staff becomes a 1/1 green Snake creature with deathtouch and loses all other abilities until end of turn.
Equip {3}

[+1]: You may sacrifice a permanent. If you do, each opponent sacrifices a permanent that shares a type with it.
[–2]: Put target creature card in a graveyard onto the battlefield under your control.
[–8]: You control target player during their next turn. During that turn, that player may cast spells by paying life equal to their mana value rather than pay their mana cost. After that turn, that player takes an extra turn.

For each permanent type, you may put a permanent card of that type from your hand onto the battlefield. Exile Set the Stage.

Menace
When Setar Ritualist enters or whenever you cast a spell, if {U}{R} was spent to cast it, Setar Ritualist deals 3 damage to target permanent, then tap that permanent. Put a +1/+1 counter on Setar Ritualist.

Equipped creature gets +2/+2 and has ward {2} and “Whenever this creature attacks, draw a card, then you may put a land card from your hand onto the battlefield.”
Equip {2}

Enchant player
At the beginning of enchanted player's upkeep, that player creates a 1/1 white Soldier creature token.

Settle the Dust deals 4 damage to each tapped creature.