msem-instigator

At the beginning of combat on your turn, target creature you control with flying gets +1/+1 until end of turn.

Slipsand Oasis enters the battlefield tapped unless you played it from exile.
{T}: Add {W} or {B}.

Slipstream Horizon enters the battlefield tapped.
{T}: Add {U} or {R}.
{U}{R}, {T}, Sacrifice Slipstream Horizon: Conjure a card named Data-Point into your hand. (It's a sorcery that costs {2} with “Draw a card.”)

(Transform this if it's not attached to a creature. Pay {2}{W} as a sorcery to unattach it.)
Enchant creature you control
Slopestrider's Chariot's rider gets +1/+1 and has double strike.

{T}: Add {C}.
{4}, {T}, Sacrifice Slyten Crystal Motherlode: Add {W}{U}{B}{R}{G}.

{T}: Add {C}.
{T}: Add one mana of any color. You can't spend this to cast spells from your hand.

Snow Drift enters the battlefield tapped. When it does, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this, then you may put that card into your graveyard.)
{T}: Add {U}.
{4}{U}: Snow Drift becomes an Elemental creature. (This effect lasts indefinitely.)

{T}: Add {C}.
{T}, Pay 1 life: Add {R} or {W}.

{T}: Add {C}. If Soaring Observatory entered the battlefield this turn, add one mana of any color instead.
Tap three differently named untapped Academies you control: Add three mana in any combination of colors.

({T}: Add {G} or {U}.)
Soaring Rainforest enters the battlefield tapped.
{1}, {T}: Add {G}{G} or {U}{U}.

({T}: Add {U} or {B}.)
Sodden Cavern enters the battlefield tapped.

Lifelink
When you attain Sojourner of the Beyond, create two 1/1 white Spirit creature tokens with flying. They gain haste until end of turn.

{T}: Add {C}.
Satrapies you control have “{1}{W}, {T}, Exile a card from your graveyard: Create a 1/1 white Soldier creature token.”

Soli Sanctuary enters the battlefield tapped.
Satrapies you control have “{T}: Add {W} or {U}.”

Soli Temple enters the battlefield tapped.
Satrapies you control have “{T}: Add {G} or {W}.”

({T}: Add {B} or {G}.)
Somber Marsh enters the battlefield tapped.

Somber Meadow enters the battlefield tapped.
{T}: Add {W} or {B}.
{1}, {T}: Add one mana of any color.

Whenever equipped creature attacks or blocks, you gain 2 life.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

{T}: Add {C}.
{T}: Add one mana of any color among planeswalkers you control.
{1}, {T}: Put a loyalty counter on target planeswalker that activated a loyalty ability this turn.

Sparring Ground enters the battlefield with a +1/+1 counter on it.
{T}: Add {C}.
Whenever a creature enters the battlefield under your control, you may move a +1/+1 counter from Sparring Ground onto that creature.

Spawning Barrens enters the battlefield tapped unless you have 15 or less life.
{T}: Add {B} or {R}.

Creatures your opponents control can't block alone. (They can block different creatures.)

Spined Spire enters the battlefield tapped.
{T}: Add {U} or {R}.
{1}{U}{R}: Until end of turn, Spined Spire becomes a Lizard creature with menace in addition to its other types.
Scavenge {1}{U}{R}

Spinerock Canyon enters the battlefield tapped unless you control a basic land.
{T}: Add {R} or {W}.