msem-instigator

If a creature entering causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.
[+1]: Target player draws two cards, then discards a card. Put a +1/+1 counter on up to one target creature you control.
[–3]: Create a token that's a copy of target creature you control.
[–8]: Return any number of target nonland permanents to their owner's hand.

[+1]: Scry 2. Whenever one or more creatures you control deal combat damage to a player this turn, draw a card.
[–2]: Create a token that's a copy of target creature you control, except the token is 4/4 and has vigilance.
[–7]: You get an emblem with “At the beginning of your draw step, draw two additional cards” and “Creatures you control get +1/+1 for each card you've drawn this turn.”

When Makshi, Patron of Blades enters, search your library for an Equipment card, reveal it, put it into your hand, then shuffle. Add {W}{U}{B}{R}{G}. Spend this mana only to cast Equipment spells and activate abilities of Equipment.

Nonenchantment spells cost {1} more to cast.
Whenever you cast an enchantment spell, you gain 1 life and draw a card.

Prowess
When Maktali Visionary enters, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

{T}, Discard a card: Draw a card.
{1}, {T}, Discard a card: Scry 2, then draw a card.
{4}, {T}, Discard a card: Search your library for a card, put it into your hand, then shuffle.

Enchant creature
Enchanted creature gets -X/-X, where X is 1 plus the number of counters on it.

Return target creature card with mana value 5 or less from your graveyard to the battlefield.
Metamorph {B} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up and cast it at any time for its metamorph cost.)

This spell costs {2} less to cast for each Curse you control.
Flying, vigilance, haste

[+2]: Up to one target creature gains deathtouch until your next upkeep.
[–3]: Target player sacrifices a creature and discards a card.
[–8]: Exile all creature cards from all graveyards, then create an X/X black Horror creature token with indestructible, where X is the total power of creatures exiled this way.

Haste
Whenever Malformed Mongrel deals combat damage to a player, discard a card.

All creatures get -2/-2 until end of turn. If a creature an opponent controls would die this turn, exile it instead.

When Malicious Growth enters and at the beginning of your upkeep, put two +1/+1 counters on target land you control.
{1}{G}: Target land you control becomes a 0/0 Elemental creature with haste and vigilance until end of turn. It's still a land.

Enchant creature
Enchanted creature has first strike and trample.

Destroy target artifact, enchantment, or planeswalker.
Orchestrate—{G}, Sacrifice a land. (You may exile this card from your hand anytime you could cast a sorcery for its orchestrate cost. When you next resolve a spell, you may cast this from exile without paying its mana cost.)

Enchant creature
Enchanted creature gets +2/+0.
When Malignance is put into a graveyard from the battlefield, return Malignance to its owner's hand.
Lifecycle {3} ({3}, Discard this card: Create two tapped 1/1 colorless Elemental creature tokens.)

Whenever Malignant Afflicted perseveres, destroy target creature an opponent controls that dealt damage this turn. (A creature perseveres when it survives damage.)

{2}: Exile up to two target cards in a single graveyard. If two creature cards were exiled this way, create a 1/1 blue Elemental creature token with flying.

Put any number of target creature cards from your graveyard on top of your library.
You draw two cards, and you lose 2 life.

Haste (This creature can attack and {T} as soon as it comes under your control.)
Double strike (This creature deals both first-strike and regular combat damage.)

Flying, vigilance
Exile a creature card from your graveyard: Maligned Scavenger gets +1/+1 until end of turn.

Lifelink
When this creature enters, put a -1/-1 counter on a creature you control.

Enchant creature
Enchanted creature gets -3/-3.

Whenever a non-Serf creature you control enters, create a 0/1 black Serf creature token.
Sacrifice a Serf: Target creature you control gets +0/+1 until end of turn.

Dominance — When Mammoth Crab enters, draw a card if you control the creature with the greatest power or tied for the greatest power.