msem-instigator

When Escorted Ambassador enters, create two 1/1 white Robot Soldier artifact creature tokens.
Whenever a nonland, nontoken permanent enters, exile it unless it was the first to enter under its controller's control this turn.

Whenever one or more other creatures you control enter, you gain 1 life. If at least one of those creatures was a Cleric, you gain 2 life instead.
As long as you have at least 8 life more than your starting life total, other Clerics you control get +1/+1.

Whenever Fox of the Mushroom Forest enters or deals combat damage to a player, its activated abilities cost {W} less to activate until your next turn.
{W}, Sacrifice Fox of the Mushroom Forest: Counter target noncreature spell unless its controller pays {2}.

Whenever you cast a legendary spell or play a legendary land, put a +1/+1 counter on Henros, Royal Herald and you gain 1 life.
{2}{W}: Look at the top six cards of your library. You may exile a legendary card from among them. Then shuffle. If the exiled card has mana value less than Henros's power, you may put it onto the battlefield tapped. If you don't, put it into your hand.

Herald of the Yaoguai has indestructible as long as two or more creatures you control entered this turn.

Lifelink
When Hyctaleon's Vanguard enters, look at the top six cards of your library. You may put a Soldier card with lesser mana value from among them onto the battlefield. Put the rest on the bottom of your library in a random order.
Other Soldiers you control get +1/+1.

Enchant creature
Enchanted creature gets +1/+1, has flying and lifelink, and is a legendary artifact in addition to its other types.

Exile up to one target nonland permanent you control and up to one target nonland permanent card with mana value 3 or less from your graveyard. Then return the exiled cards to the battlefield tapped under their owner's control.

Flash
Flying
When Justiciar Overseer enters, the next 2 damage that a source of your choice would deal to you and/or permanents you control this turn is dealt to any target instead.

Whenever you gain life for the first time each turn, create a 1/1 white Cleric creature token.

Other creatures you control get +1/+1.
When Kotis, Promised General dies, you may return it to its owner's hand.

Whenever you gain life, Militant Youth gets +1/+1 until end of turn.

When Prized Holsteins enters, create a 2/2 white Dwarf creature token.
When Prized Holsteins leaves the battlefield, you gain 2 life.

Enchant creature
Enchanted creature can't attack or block.
Foresee — As you draw Prophecy of Peace, you may reveal it and pay {W}. When you do, target creature can't attack or block this turn.

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.

Enchant creature
When Sprawled Arming enters, put a +1/+1 counter on enchanted creature.
Enchanted creature has first strike.
{5}: Return Sprawled Arming to its owner's hand.

Whenever you attack, create a white Equipment artifact token with “Equipped creature gets +1/+1” and equip {1}. Attach it to an attacking creature you control.
At the beginning of your end step, untap each embattled creature you control. (A creature is embattled if it has a counter on it or has a permanent you control attached to it.)

Create two 1/2 blue Bird creature tokens with flying.
Coalesce {5}{U}{U} (You may cast this from your graveyard for {5}{U}{U}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
When Dancer of the Great Current enters, tap up to one target creature. If you control two or more other creatures that are Merfolk, Wizards, or Rogues, instead return that creature to its owner's hand and put a +1/+1 counter on Dancer of the Great Current.

At the beginning of your upkeep, each opponent mills cards equal to the number of card types among permanents you control.

Counter target spell unless its controller pays {1}. If you control a creature with flying, counter that spell unless its controller pays {4} instead.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
Whenever Manipulator of Waves attacks, mill three cards. Then create a 0/0 blue Elemental Serpent creature token with “This creature gets +1/+1 for each five cards in your graveyard.”

Prowess
Whenever you cast your first noncreature spell during each of your turns, create a 1/1 blue Reflection Wizard creature token with prowess.

Draw two cards, then discard two cards. Then if you cast Price of Wisdom from your graveyard, create a 3/3 blue Sphinx creature token with flying.
Flashback {4}{U}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)