msem-instigator

Flash
When Scholar of Reflections enters, you may switch target creature's power and toughness 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 Sheltered Diviner enters, each player mills three cards.

Shimmering Seadragon gets +1/+0 and can't be blocked as long as you control a legendary creature.

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Marked creatures your opponents control lose all abilities.

{1}, {T}: Surveil 2.
{U}, {T}, Discard a card: Look at the top card of your library. If it's a nonland card, you may cast it. (You still pay its costs)

Whenever you cast a noncreature spell, Slyten Technician gets +1/+0 until end of turn, then scry 1.

Whenever a permanent you control leaves the battlefield, if it had counters on it, you may put those counters on Stage Magician.
At the beginning of your end step, you may move any number of counters from Stage Magician onto target permanent you control.

{T}: Look at the top two cards of your library, then put them back in any order.

At the beginning of each end step, if you've cast a noncreature spell this turn, put a +1/+1 counter on Streetwise Spellseeker. Then if its power is 5 or greater, create a 4/4 white Angel Soldier creature token with flying.

Whenever you create a token, Substack Runner gets +1/+0 and can't be blocked until end of turn.

You may have Sun Yun enter as a copy of any creature on the battlefield, except her name is Sun Yun, Master of Man, she's legendary in addition to her other types, and she has “{2}{U}: Exile Sun Yun, then return her to the battlefield under her owner's control.”

If a creature entering the battlefield under your control causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.
{1}{U}, {T}: Exile another target creature. Return it to the battlefield under its owner's control at the beginning of the next end step.

Prowess
When Surviving Scavengers enters, you may draw a card, then discard a card.

Ward {2}
Even numbered spells you cast each turn costs {2} less to cast. (The second, fourth, sixth, etc.)

When Truthseeker Prodigy enters, amass Soldiers 2. Then target player mills X cards, where X is the amassed Army's power. (To amass Soldiers 2, put two +1/+1 counters on an Army you control. It's also a Soldier. If you don't control an Army, create a 0/0 black Soldier Army creature token first.)

Rhapsody {4}{U}{U} (Pay {4}{U}{U} to cast this as a 4/4, or as a sorcery to make it become a 4/4.)
When Unstable Prophet enters, surveil X, where X is its power. (Look at the top X cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
When Ushi Yun enters, create an Idol token.
As long as you're in a renaissance, artifacts you control have “{T}: Draw a card.”

When Veiled Transmuter enters, you may cast an instant or sorcery card with mana value 2 or less from your hand without paying its mana cost.
Magecraft — Whenever you cast or copy an instant or sorcery spell, create a 2/2 blue Reflection creature token.

{T}: Add {C}. Spend this mana only to cast an instant or sorcery spell or activate an ability.
{2}{U}: Move a counter from target creature onto another target creature.

Whenever you sacrifice a Clue, Vivian's Vanguard gets +2/+0 and gains flying until end of turn.

Flying
When Windwielder enters, you may return target Inscription card from your graveyard to your hand.

Whenever you cast a noncreature spell, look at the top X cards of your library, where X is that spell's mana value. Put those cards on top of your library in any order.