msem-instigator

Draw three cards, then manifest a card from your hand. (To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)

Flash
When Scholar of Reflections enters, you may switch target creature's power and toughness until end of turn.

Flying
{1}{U}, Sacrifice Scholar's Assistant: Draw a card.

Attacking creatures get -3/-0 until end of turn.

Flying
When Scion of Torrents enters, you may return target nonland permanent to its owner's hand.
Whenever an Island you control enters, you may aetherize Scion of Torrents. (To aetherize, create a token that's a copy of it, then exile that token.)

Counter target spell with no subtypes. Surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)

(Add a quest counter as this enters. Sacrifice after 3.)
Whenever you cast a noncreature spell, add a quest counter.
Draw a card, then discard a card.
Return up to two target instant and/or sorcery cards from your graveyard to your hand.
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Flying
Dragon spells and Adventure spells you cast cost {1} less to cast.

Counter target permanent spell. (Then exile this card. You may cast the creature later from exile.)

Whenever you cast an instant or sorcery spell, put a +1/+1 counter on Scribe of the Sky Scrolls. If you spent four or more mana to cast that spell, Scribe of the Sky Scrolls gains flying until end of turn.

When Scrivener of Sha'Iv enters, draw a card and adjudicate. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)

When Scrollmaster dies, you may exile it. If you do, search your library for an instant or sorcery card with mana value 4 or less and cast it without paying its mana cost. If you searched your library this way, shuffle.

At the beginning of your upkeep, if six or more cards are in your graveyard, you may transform Scuttling Gnat.

Draw a card, then draw cards equal to the number of cards named Sea Cache in your graveyard.

When Sea Hunter enters, you may return target creature with mana value 4 or greater to its owner's hand.

Sea Of Skies Beyond enters tapped.
Whenever you cast a noncreature spell, put a creation counter on Sea Of Skies Beyond.
{T}, Remove ten creation counters from Sea Of Skies Beyond and sacrifice it: Shuffle your hand into your library, then draw five cards.

{U}: Sea Strider gets +1/-1 until end of turn.
{U}: Sea Strider gets -1/+1 until end of turn.

Defender
{1}{U}: Sea Wall gets +0/+1 until end of turn.
Whenever Sea Wall perseveres, you may return target creature an opponent controls to its owner's hand. (A creature perseveres when it survives damage.)

Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
When Sea's Allure enters, gain control of target creature for as long Sea's Allure remains on the battlefield.

Flash
When Seabreen Nullmage enters, counter target activated or triggered ability. (A triggered ability uses the words “when,” “whenever,” or “at”. Mana abilities can't be targeted.)

When Seafloor Casket enters and when you sacrifice it, target player mills two cards.
{1}{U}, Sacrifice Seafloor Casket: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

Flash
{U}, Sacrifice Seal of Approval: Counter target spell unless its controller pays {2}.

{U}, Sacrifice Seal of Insights: Look at the top four cards of your library. Put one into your hand and the rest on the bottom of your library in any order.

Reveal the top five cards of your library. You may put an instant or sorcery card from among them into your hand. Put the rest into your graveyard.