msem-instigator

Whenever you draw a card, you may have target opponent exile the top card of their library face down.
You may look at and play cards exiled with Thought Siphon, and you may spend blue mana as though it were mana of any color to cast them.

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast your first instant or sorcery spell each turn, copy that spell. You may choose new targets for the copies.

Flying
Wailing Soul has hexproof as long as it's not attacking or blocking.

Whenever Waketide Serpent attacks, you may pay {2}{U}. If you do, tap target creature. It doesn't untap during its controller's next untap step.

Flying

Whenever Abyssal Stalker attacks, defending player discards a card at random.
When Abyssal Stalker dies, you may choose a creature. If you do, exile Abyssal Stalker. When the chosen creature leaves the battlefield, return Abyssal Stalker from exile to the battlefield tapped.

{2}{B}, {T}, Discard a card: Create a 2/2 black Zombie creature token. If a noncreature card was discarded this way, that token enters the battlefield tapped.

Destroy target tapped creature.

Menace (This creature can't be blocked except by two or more creatures.)
Blood Fiend can't block.
{1}{B}, Pay 3 life: Return Blood Fiend from your graveyard to the battlefield. It gains haste.

When Caustic Lurker dies, target player loses 1 life.

Menace
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Enchant creature
Enchanted creature gets +3/-2.

When Dark Bargain enters the battlefield, you draw a card and you lose 1 life.
{B}, Sacrifice Dark Bargain: You draw a card and you lose 1 life.

Destroy four target creatures.

Target player discards a card. If that player discards a land card this way, they lose 3 life.

Exile target creature and all other creatures with the same name as that creature. Search its controller's graveyard, hand and library for any number of cards with the same name as that creature and exile them. Then that player shuffles. Exile Erase from Existence.

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

As an additional cost to cast this spell, discard a card.
Search your library for a card with mana value X or less, where X is 1 plus the discarded card's mana value, reveal it, put it into your hand, then shuffle.

As an additional cost to cast this spell, sacrifice a creature.
Target creature gains +4/+4 until end of turn.

Flying (This creature can't be blocked except by creatures with flying or reach.)
When Lord of Swarms enters the battlefield or dies, target creature gets -2/-2 until end of turn.

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Mausoleum Revenant deals damage to a player, create a 2/2 black Zombie creature token.

Target player reveals their hand. You choose three cards from it and exile them. Then that player exiles the top three cards of their library.

Target creature you control gets +1/+0 and gains menace until end of turn. (That creature can only be blocked by two or more creatures.)
Draw a card.

Return up to two target creature cards from your graveyard to your hand.