msem-instigator

Flash
If a card or token would be put into an opponent's graveyard from anywhere, exile it instead.

Exile target instant or sorcery card from your graveyard. Copy it. You may cast the copy. (Cast a copy of this spell once while this creature is on the battlefield.)

Create an X/X green and blue Plant creature token, where X is the number of differently named lands you control.

Prowess

Each player puts the bottom five cards of their library into their graveyard.
Fuse (You may cast one or both halves of this card from your hand.)

Whenever High-Priestess Nebti attacks or blocks, create a 2/2 white Cat creature token.
{1}{R}{R}, Tap an untapped Cat creature you control: That creature fights target creature you don't control.

Each player sacrifices a creature and discards a card.
Fuse (You may cast one or both halves of this card from your hand.)

Choose one —
• Exile target player's graveyard.
• Target player sacrifices a creature.

Return target creature card with mana value 3 or less from your graveyard to the battlefield. Put a +1/+1 counter on it. It gains indestructible until end of turn.

Concord — This spell costs {4} less to cast if there are four or more card types among permanents you control.
Vigilance, trample, lifelink, haste

Target creature gets +2/+1 and gains trample until end of turn. Create a tapped Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Whenever you make first contact, Abrasive Citizen gets +3/+0 until end of turn. (You make first contact the first time each turn you cast a spell with a name not in your graveyard or control already.)

Abyss Howler must be blocked if able.
Whenever Abyss Howler becomes blocked, defending player loses 2 life and you gain 2 life.

Wither (This deals damage to creatures in the form of -1/-1 counters.)
Abyssal Accuser must be blocked if able.

Wither (This deals damage to creatures in the form of -1/-1 counters.)
When Abyssal Familiar dies, it deals 1 damage to you and to any target.

When Abyssal Pact enters, you draw two cards and each player loses 2 life.
Players can't gain life.
Damage can't be prevented.

Death knell — Each opponent loses 1 life. You gain life equal to the amount of life lost this way. (As a creature you control dies, trigger one death knell of that creature or another permanent you control.)
Whenever a creature dies, trigger a death knell of a permanent you control.

Gain control of target creature until end of turn. Untap that creature. It gains haste until end of turn.
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.)

Deception {1}{B}
When Aguri, Shadow of Doubt enters, target player reveals their hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

[+1]: Aiel Tazan deals 2 damage to any target. Then she deals 2 damage to herself unless you have her deal 2 damage to you.
[–3]: Creatures you control get +2/+0 and gain haste until end of turn.
[–X]: Create an X/1 red Elemental creature token with haste and trample. Exile that token at the beginning of the next end step. If X is 6 or more, it gains double strike.

You have no maximum hand size.
{T}: Add {C}.
{3}, {T}: Create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)

{T}: Add {C}.
{T}, Sacrifice Alchemist's Abode and another permanent: Draw a card. Activate only during your turn.

Enchant player
At the beginning of enchanted player's upkeep, if they control two or more creatures and/or planeswalkers, they sacrifice a creature or planeswalker.

Enchant creature
Enchanted creature gets +2/+2.
Whenever enchanted creature attacks, if it's a Scout, scry 2.

({T}: Add {U}, {R}, or {W}.)
Ancient Dominion enters tapped.