msem-instigator

Whenever two or more creatures you control deal combat damage to a player, you gain 3 life and create a Treasure token. (It's an artifact with “{T}, Sacrifice this permanent: Add one mana of any color.”)
Whenever you sacrifice your second permanent each turn, you draw a card and you lose 1 life.

{1}{R}{W}: Create a 2/1 red and white Fox creature token. It gains haste. Sacrifice it at the beginning of the next end step.
Whenever Fox of a Brisk Autumn attacks, attacking Foxes you control get +1/+1 until end of turn.

Whenever a creature attacks you, tap that creature. It doesn't untap during its controller's next untap step.

Search your library for a creature or planeswalker card, reveal it, put it into your hand, then shuffle.

You may cast Gateblessed Explorer from your graveyard as long as you control three or more creatures.
Whenever another creature dies, each opponent loses 1 life and you gain 1 life.

{1}{U}{R}, {T}: Create a token that's a copy of another target creature, except it's an artifact in addition to its other types and has “Whenever this creature is dealt damage, destroy it.”

{T}: Draw a card, then discard a card.
Sacrifice Ghislain, Cryptbreaker: You may cast target creature, instant or sorcery card from your graveyard this turn. If that spell would be put into your graveyard, exile it instead. Activate only during your turn.

Return target creature card with mana value 3 or less from your graveyard to the battlefield. It gains haste until end of turn.
Monument {3}{B}{R} (You may cast this transformed from your graveyard for its monument cost. Exile it if it would leave the battlefield or not resolve.)

Creatures you control get +1/+1 and gain trample and lifelink until end of turn.

Sacrifice a creature. At the beginning of the next end step, return that card from a graveyard to the battlefield under your control with two +1/+1 counters on it, except it's a black Demon instead of its other colors and types.

Rouse 2, then you gain 1 life for each creature you control. (Distribute two +1/+1 counters among permanents you control. If they aren't creatures, tap them and they become 0/0 creatures in addition to their other types.)

Gestalt (When this or another creature enters under your control, you may merge it with the one in play, keeping counters and attachments. They become the permanent on top plus all abilities from under it.)
This creature gets +2/+2 and has trample as long as it's merged with another card or token.

Destroy target creature or planeswalker if damage has been dealt to it this turn. Then Give to Sacred Halls deals 1 damage to it.
Acquiesce (If you cast this spell from your hand, exile it as it resolves. When one or more creatures you control deal combat damage to an opponent, you may cast this card from exile without paying its mana cost.)

Trample
At the beginning of each combat, you may have Grisly Offering deal 3 damage to target creature you control. If you do, Grisly Offering gets +3/+0 until end of turn.

Creature spells you cast cost {1} less to cast.
Whenever you attack, target attacking creature you control gets +1/+1 until end of turn. If it's legendary, put a +1/+1 counter on it instead.

You may look at the top card of your library any time.
{T}: Reveal the top card of your library. If that card has a creature type no creature you control has, put it into your hand.

Refine {3}{W}{B} (You may cast this spell by sacrificing an artifact and paying the refine cost reduced by that artifact's mana value.)
When H-9K Prototype enters the battlefield, if it was refined, destroy target nonland permanent.

Whenever one or more creature cards leave your graveyard, Hadik's Cohort deals 2 damage to target opponent.

Augmented — Whenever you cast a spell from your hand, if you've spent {W}{U}{B}{R}{G} to cast spells this turn, exile cards from the top of your library until you exile a nonland card with mana value less than that spell's mana value. You may cast that card without paying its mana cost. Put the exiled cards not cast this way on the bottom of your library in a random order.

Whenever Heedless Astronaut attacks, it gets +2/+0 and gains indestructible until end of turn.

When Heirloom Seeker enters the battlefield, you may search your library for an Equipment card, reveal it, then shuffle your library and put that card on top of it.
Heirloom Seeker has first strike as long as it's equipped.

Flying, lifelink, haste
At the beginning of the end step, sacrifice Helix Entity.

[–1]: Tap target nonland permanent. It doesn't untap during its controller's next untap step.
[–2]: Put target nonland permanent into its owner's library second from the top.
[–X]: Shuffle up to X cards from your hand into your library, then draw that many cards. You gain that much life.

Whenever a Project enters the battlefield under your control, create two 1/1 colorless Construct artifact creature tokens.
Whenever a creature leaves the battlefield, you may put a progress counter on a Project you control.

Haste
Herald of Unity's power is equal to the number of creatures you control.