msem-instigator

Lost Explorer has first strike as long as it's attacking.
{1}{B}, Exile Lost Explorer from your graveyard: Crystallize. (Put a +1/+1 counter on a creature you control or create a Treasure.)

Exile target nonland permanent.

Love Letters enters with X stamp counters on it.
Whenever one or more creatures you control deal combat damage to a player, you may remove a stamp counter from Love Letters. If you do, draw a card.

When Lust for Life enters, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
Augmented — Whenever a creature you control enters, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, you may sacrifice Lust for Life. If you do, create a token that's a copy of that creature.

When Lysander Jal enters, create a token that's a copy of another target noncreature permanent you control.
Whenever you cast a spell from your graveyard, return target permanent card from your graveyard to your hand.

For each of up to X target creature cards in your graveyard, create a token that's a copy of it. Exile the tokens at the beginning of the end step.

Enchant creature
When Mantle of the Returned enters, return target creature card from your graveyard to the battlefield. It's a Zombie in addition to its other types.
Enchanted creature gets +1/+1 for each Zombie you control.

Whenever an artifact you control enters, Master of Munitions deals 1 damage to each opponent.

Target creature you control gets +1/+0 until end of turn. It fights up to one target creature you don't control. (Each deals damage equal to its power to the other.)

Meletian Trireme can't be blocked by creatures with power 2 or less.
Whenever Meletian Trireme enters or deals combat damage to a player or planeswalker, scry 1, then draw a card.
Crew 2 (Tap any number of creatures you control with total power 2 or greater: This Vehicle becomes an artifact creature until end of turn.)

When Meletis Oracle enters, scry 1, then draw a card.

Heroic — Whenever you cast a spell that targets Meletis Stargazer, scry 2.
{T}: Look at the top card of your library. If it's a permanent card with mana value 3 or less, you may reveal it and put it into your hand.

Flash
Flying
When Meletis Stratomancer enters, target creature an opponent controls gets -2/-0 until end of turn.

When Memento Gorgon enters, mill X cards, where X is your devotion to black. Then return a card milled this way to your hand. You lose 1 life. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Reverberate {2}{U}{R} (When you cast this spell, copy it if you paid its reverberate cost. You may choose new targets for the copy.)
Exile target instant or sorcery card from your graveyard. You may cast a copy of that card without paying its mana cost.

Whenever Memory of Fatalism dies or you cast a noncreature spell, each opponent loses 2 life and you gain 2 life.
{4}: Put Memory of Fatalism from your graveyard on top of your library.

Counter target spell unless its controller pays {2}. If that spell targets you or a permanent you control, counter that spell instead.

Whenever a land you control enters, crystallize.
{10}: Shuffle any number of other permanents you control into their owner's library. Mill that many cards. Put all permanent cards milled this way onto the battlefield. Activate only during your turn and only once each turn.

Enchant creature you control
When Military Authority enters, create two 1/1 white Soldier creature tokens.
Enchanted creature gets +2/+2.

Counter target spell. Search its controller's library for a card with mana value X or less and cast it without paying its mana cost. Then that player shuffles.

When Mineral Expert enters, surveil 1. When you do, you may return target instant or sorcery card from your graveyard to your hand. (Look at the top card of your library. You may put that card into your graveyard.)

Colossal 3—{6}{R} (You may cast this for its colossal cost to have it enter with three +1/+1 counters; or pay {6}{R} as a sorcery: Put three +1/+1 counters on it if it has none.)

Menace
When Minotaur Skullsmasher enters, choose a nonland card type. Then target opponent reveals their hand. You choose a card of the chosen type from it. That player discards that card.

Heroic — Whenever you cast a spell that targets Mira and Kalisti of Akros, copy that spell. You may choose new targets for the copy. (The copy isn't cast. A copy of an Aura spell becomes a token.)

Deathtouch
When Mire Triton enters, mill two cards and you gain 2 life.