msem-instigator

Counter target spell unless its controller pays {X}. Look at the top X cards of your library. Put up to one of them on top of your library and the rest on the bottom of your library in a random order.

Whenever a land you control enters, you gain 1 life.
{3}{G}, Sacrifice Sower of Spring: Search your library for up to two basic land cards, put them onto the battlefield tapped, then shuffle.

Exile the top card of your library. You may have Spark Inspiration deal 2 damage to each opponent. If you don't, you may play that card until end of turn.

{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.

{2}: Sparkline Dancer gains flying until end of turn.

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

Spawn of Andazir enters with X +1/+1
counters on it.
Lionize {2}{G} ({2}{G}, Exile this card from your hand:
Put a +1/+1 counter on target creature and it gains the following ability until end of turn. You may cast this card on a later turn from exile.)
Whenever this creature deals damage to a player or noncreature permanent, double the number of +1/+1
counters on it.

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

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
If you would gain life, you may put a +1/+1 counter on this creature instead.
When this creature has toughness 20 or greater, you win the game.

Spearhead deals X damage to target player. (Then exile this card. You may cast the creature later from exile.)

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

When Specialized Training Dummy enters, choose a card name.
Other creatures you control with the chosen name get +1/+1.

Choose one —
• Target creature gets +2/+2 and gains indestructible until end of turn if it has flying.
• Target creature gets +1/+1 and gains flying until end of turn.

Counter target noncreature spell unless its controller pays {2}.

Enchant creature
When Sphinx's Advice enters, draw a card.
Enchanted creature has flying.

Once each turn, when one or more cards are put into an opponent's graveyard from their library, you may draw a card.

Spined Spire enters 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 tapped unless you control a basic land.
{T}: Add {R} or {W}.

Haste
Ward—Sacrifice a creature.
Spinning Gears Abomination enters with X +1/+1 counters on it.
Spinning Gears Abomination can't attack alone.

Spiny Ridge enters 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 {R}.
{4}{R}: Spiny Ridge becomes a Lizard creature. (This effect lasts indefinitely.)

({T}: Add {R} or {W}.)
Spiraling Canyon enters tapped unless you control a basic Mountain or a basic Plains.

({T}: Add {R}.)
Spire Sanctuary enters tapped with two sanctum counters on it.
{T}, Remove a sanctum counter from Spire Sanctuary: Add {B} or {G}.

Spired Canopy enters tapped unless another player controls a land that could produce {G} or {U}.
{T}: Add {G} or {U}.

Spires of Caulte enters tapped.
{T}: Add {B} or {R}.
{B}{R}: Until end of turn, Spires of Caulte becomes a 3/2 black and red Construct creature with with menace and “Whenever this creature attacks or blocks, torment yourself.” It's still a land. (To torment yourself, lose 3 life unless you discard a card or sacrifice a nonland permanent.)

{T}: Add {C}.
{T}, Exile two cards from your graveyard: Add {W} or {U}.