msem-instigator

This spell costs {1} less to cast for each legendary creature you control.
Search your library for a legendary creature card with mana value X or less, put that card onto the battlefield, then shuffle.

Trample
Avatar of the Groves enters the battlefield with a +1/+1 counter on it for each land you control.
Landfall — Whenever a land enters the battlefield under your control, proliferate. (Choose any number of permanents and/or players with counters on them, then give each another counter of each kind already there.)

Faux, Who Lives for the Hunt enters the battlefield as a copy of a creature card in your graveyard except it's legendary and has changeling and “When this creature dies, if it didn't have a bounty counter on it, return it to the battlefield with a bounty counter.” (It has “When this creature dies, each opponent draws a card” as long as it has a bounty counter on it.)

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

Trample
Whenever a creature card is put into your graveyard from anywhere, put a +1/+1 counter on Jawbone, Ravenous Mutant.

Lifelink, first strike
You may cast creature spells from your graveyard if their mana value is less than or equal to the amount of life you have gained this turn. Whenever you cast a creature spell this way, it enters the battlefield with a finality counter on it.

When Rixia, Rift Shunted enters the battlefield, target creature can't be blocked this turn.
Whenever a creature you control deals combat damage to an opponent, you may aetherize it. (To aetherize, create a token that's a copy of it, then exile that token.)

Flying
When Spectre of Terror deals combat damage to a player, that player discards a card.
Madness {1}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Flying
Whenever one or more other creatures die for the first time each turn, journey. (To journey, exile the top card of your library face up. Whenever a creature you control deals combat damage to an opponent, put a journeyed card you own into your hand.)

[+1]: Until end of turn, Winmeari, Glorian Defector becomes a 5/5 Warrior creature with lifelink that's still a planeswalker. Prevent all damage that would be dealt to her this turn.
[0]: Create a 2/2 black Zombie creature token.
[–1]: You get an emblem with “Attacking creatures your opponents control must attack a Winmeari planeswalker if able.”