msem-instigator

{5}, {T}, Sacrifice Mennin Jar: Destroy target permanent. Its controller creates a 1/1 black Goblin creature token.

Flash
When Mennin Pack enters, each opponent loses 1 life.
When Mennin Pack dies, each opponent discards a card.

Create X 1/1 black Goblin creature tokens. Gain control of target permanent with mana value X or less until end of turn. Untap it. It gains haste until end of turn.

Untap all nonland permanents you control.
Agonize (You may cast this card from your graveyard by putting a -1/-1 counter on a creature you control in addition to paying its other costs. Then exile this card.)

Target player mills six cards.
Draw a card.

Return target nonland permanent to its owner's hand. That player mills two cards.

Flash
Enchant instant or sorcery spell
Enchanted spell's text box is “This spell deals 3 damage to you.”
{4}{U}{U}{R}{R}: Return Mental Meltdown from your graveyard to the battlefield.

When Mental Supremacist enters, choose target creature you don't control. That creature has base power and toughness 1/1 and loses all abilities for as long as you control Mental Supremacist.

Until end of turn, you may play cards you don't own from exile. Scry 1.

Other Elementals you control get +2/+2.
Whenever one or more Elementals you control attack, tap up to one target creature you don't control.

Whenever another creature with power 4 or greater you control enters, you may draw a card.

Activated abilities you control cost up to {1} less to activate. This effect can't reduce the amount of mana an ability costs to activate to less than one mana.

Menace

Enchant opponent
Whenever a creature enters under enchanted player's control, that creature gets -0/-2 until end of turn unless that player pays 2 life.

As Mercantile Accords enters, choose a number.
Whenever an opponent casts a spell with the chosen mana value, you draw a card and create a Treasure token.

{T}: Add {C}.
Satrapies you control enter untapped.

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Mercenary Coercer deals combat damage to a player, that player discards a card.

Adorned — Mercenary Lancer gets +2/+2 as long as it's equipped and/or enchanted.

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
{2}{B}, Discard a card: Mercenary of the Folded Fan gains indestructible until end of turn. Tap it. If you're in a renaissance, draw a card.

Crew 3 (Tap any number of creatures you control with total power 3 or greater: This Vehicle becomes an artifact creature until end of turn.)

Deathtouch
Sacrifice a creature: Target player mills two cards.

Whenever Merchant of Flesh or another creature you control dies, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)
{B}, Sacrifice two Treasures: Each opponent sacrifices a creature.

Hexproof (This creature can't be the target of spells or abilities your opponents control.)

{T}, Sacrifice Merchant's District: Search your library for an Island or Mountain card and put it onto the battlefield tapped, then shuffle.

Draw three cards, then put two cards from your hand on top of your library in any order.