msem-instigator

Look at the top four cards of your library. You may put a land card from among them onto the battlefield tapped, then put the rest into your graveyard.

Target opponent reveals their hand. You choose a nonland card from it and exile that card.
Recruit. (Create a 0/0 white Soldier Army creature token, then put a +1/+1 counter on each Army you control.)

Target opponent reveals their hand. You choose a nonland card from it. That player exiles that card.
Each player conjures a card named Data-Point into their hand. (It's a sorcery that costs {2} with “Draw a card.”)

Prevent all damage that would be dealt by creatures this turn.

Target player discards a card. If they didn't discard an artifact card, you gain 3 life.

Embellish {3}{B} (If you cast this spell for {3}{B}, create a 1/1 blue Thopter artifact creature token with flying when it enters.)
When Scrap Spiral enters, target creature gets -2/-2 until end of turn.
{3}{B}, {T}, Sacrifice an artifact: Target creature gets -2/-2 until end of turn.

Look at the top X cards of your library, where X is the number of instant and sorcery cards in your graveyard. You may reveal an instant or sorcery card from among them and put it on top of your library. Then put the rest on the bottom of your library in a random order.

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

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Create two 1/1 white Human creature tokens.
II — Put a vigilance counter on target creature you control. It becomes a legendary God in addition to its other types.
III — Exile target creature an opponent controls that's a God or that has power 4 or greater.

As Scrolls of Succession enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
{2}, {T}: Draw a card. Then discard a card unless you control three or more creatures of the chosen type.

When Scrying Pool enters, scry 2.
{1}, {T}: Add one mana of any color.

{2}{B}, {T}, Sacrifice Sculler's Oar: Return up to two target creature cards from your graveyard to your hand.

At the beginning of your upkeep, you lose 1 life, then audition for black. (Create a 1/1 Construct Actor creature token, a Cleric Role giving 2/2 and lifelink, or a Warlock Role giving 2/1 and flying. Roles replace older ones.)

Sculpted Observatory enters tapped.
{T}: Add {W} or {U}.
{1}, {T}: Add one mana of any color.

Enchant creature
Enchanted creature gets +2/+2.
Enchanted creature has hexproof as long as it's tapped.

Until end of turn, target creature gains “When this creature is dealt damage, destroy it.” (Then exile this card. You may cast the creature later from exile.)

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

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.

This spell costs {2} less to cast for each creature that died this turn.
Each player exiles all creature cards from their graveyard, then sacrifices each creature they control, then puts all creature cards they own exiled this way onto the battlefield. Exile Sea of Corpses.

When Seafloor Cache enters and when you sacrifice it, create a Treasure token.
{1}{R}, Sacrifice Seafloor Cache: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

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.)

When Seafloor Shrine enters and when you sacrifice it, create a 1/1 white Merfolk creature token.
{1}{W}, Sacrifice Seafloor Shrine: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

When Seafloor Tomb enters and when you sacrifice it, exile up to two target cards from graveyards.
{1}{B}, Sacrifice Seafloor Tomb: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

When Seafloor Wreckage enters and when you sacrifice it, search your library for a basic land card, reveal it, put it into your hand, then shuffle.
{1}{G}, Sacrifice Seafloor Wreckage: Draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

{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.