msem-instigator

(Add a quest counter as this enters. Sacrifice after 3.)
Whenever another artifact or enchantment you control enters, add a quest counter.
1, 2 — You gain 3 life.
3 — Mill three cards, then return an artifact or enchantment card from your graveyard to the battlefield. Exile Seek the Maker's Egg.
​

As long as a creature you control has flying, creatures you control have flying. The same is true for first strike, double strike, deathtouch, haste, hexproof, indestructible, lifelink, menace, reach, trample, and vigilance.

When Seeker of Horizons enters, reveal the top three cards of your library. You may put a permanent card from among them into your hand. Put the rest on the bottom of your library in any order.
Recite {1}{U} (You may cast this creature from your graveyard for its recite cost. If you do, exile it when it enters or if it would leave the battlefield.)

Lifelink
Revelation spells you cast cost {1} less to cast.

Primal {W} (During your turn, you may cast this spell for {W} instead of playing a land.)
Destroy target attacking or blocking creature.

Enchant creature
Enchanted creature gets +2/+2.
When Seeking Horizons is put into your graveyard from anywhere other than your library, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Flying
Whenever Seer of Clear Skies or another creature you control with flying attacks, that creature gets +1/+1 until end of turn.

Spirited (When this creature enters, you may activate one of its activated abilities without paying its cost.)
{2}{W}: Create a 1/1 white Human Samurai creature token.

When Seikatsu Warleader enters, if it's not a token, create a token that's a copy of target creature token you control.

Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever a +1/+1 counter is put on Sejiri Skyhunter, it gains flying until end of turn.

Create a 1/1 colorless Construct artifact creature token. If you control an artifact, create two of those tokens instead.

When Seluriel's Blessing enters, put a +1/+1 counter on each creature you control.
Creatures you control enter with an additional +1/+1 counter on them.
Creatures you control with counters on them have vigilance and indestructible.

[+1]: You gain 1 life. Put a +1/+1 counter on up to one target creature.
[–3]: Exile target creature. Its controller gains life equal to its power.
[–8]: You get an emblem with “Creatures you control get +1/+1 and have double strike and lifelink.”

Whenever a quest counter is put on a permanent you control, upgrade Selvar, the Seeker. (Give it one of the listed counters it doesn't already have.)
• +1/+1
• First strike
• Vigilance
• Reach
• Trample
• Lifelink

When you cast Senaturian Centurion, reveal cards from the top of your library until you reveal a creature card with mana value 2 or less. Copy that card, then put the revealed card into your hand. You may cast the copy without paying its mana cost. Put the revealed cards on the bottom of your library in a random order.

Senaturian Legion gets +1/+1 for each other creature on the battlefield named Senaturian Legion.
A deck can have any number of cards named Senaturian Legion.

When Sending Stones enters, harmonize twice. (To harmonize, trigger up to one harmony of a permanent you control.)
If you would harmonize, you may trigger a harmony of a permanent card in your graveyard instead.

Choose one —
• Target permanent gains protection from instants and sorceries until end of turn.
• You gain 3 life.
• Draw a card.

Lionize {1}{W} ({1}{W}, 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.)
Flying

Equipped creature gets +2/+0. As long as it's a Knight, it has first strike.
Equip {1}{W}

Whenever Sentry of Kollis Gate is dealt damage, put a +1/+1 counter on each other creature you control.

Flying, vigilance
Whenever Sepulchral Guide attacks, prevent all combat damage that would be dealt to another target creature you control this turn. If that creature has two or more counters on it, untap it.

Whenever Ser Wayver, the Broken Hour attacks, each opponent loses 2 life and you gain that much life.
When Ser Wayver dies or is countered, exile it with three time counters on it and it gains suspend. (At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast this card without paying its mana cost. It has haste.)

Flying
When Seraph of Renewal leaves the battlefield, you may return target permanent card with mana value 3 or less from your graveyard to the battlefield.

Flying, vigilance, lifelink
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)