msem-instigator

First strike
Wither (This deals damage to creatures in the form of -1/-1 counters.)

Trample, haste
Defiance (Whenever this creature takes damage, if it survives and wasn't defiant, put a +1/+1 counter on it and it becomes defiant.)
Whenever Wastewolf attacks, it deals 1 damage to any other target.

Whenever Wasting Soul attacks or blocks, sacrifice a creature, then put two +1/+1 counters on Wasting Soul.

Whenever Watch Me Burn enters the battlefield or another source you control deals noncombat damage, put an ignition counter on Watch Me Burn. Then it deals damage equal to the number of ignition counters on it to each opponent.

Put target nonland permanent on top of its owner's library.

Creature tokens you control have vigilance.
Whenever Watch of the Dead or another enchantment enters the battlefield under your control, create a 2/2 black Zombie creature token.

Flying
Whenever a nontoken, noncreature, nonland permanent enters the battlefield under your control, create a token that's a copy of that permanent except it has no mana cost and it isn't legendary.

Changeling (This card is every creature type.)
Watcher of the Polyps has all names of creature cards in addition to its name as long as it's on the battlefield.
Watcher of the Polyps gets +X/+X, where X is the greatest number of creatures you control with the same name.

Menace
Whenever one or more cards leave your graveyard or Watchers of the Veil leaves your graveyard, you may draw a card. If you do, discard a card.

Flying

Vigilance
Whenever Watchful Navigator crews a Vehicle, that Vehicle gets +1/+1 and gains vigilance until end of turn.

Vigilance
Whenever you cast a noncreature spell, you gain 2 life.

Flying (This creature can't be blocked except by creatures with flying or reach.)
Vigilance (Attacking doesn't cause this creature to tap.)

Whenever Watchkeeper Deserter attacks, discard up to two cards, then draw that many cards. Watchkeeper Deserter gets +X/+0 until end of turn, where X is the total mana value of the discarded cards.

Remove all -1/-1 counters from target creature. That creature gets +3/+3 and gains trample until end of turn.

As an additional cost to cast this spell, discard a card.
Create three 1/1 red Soldier creature tokens with haste.

Slipstream (This creature can't be blocked as long as only creatures with slipstream are attacking.)
{3}{U}: Target creature gains slipstream until end of turn.

Prowess
Whenever you cast a noncreature spell, target creature can't block this turn.

Whenever Wavering Sorcerer attacks, you may switch its power and toughness until end of turn.
Unveil {3}{U}{R} ({3}{U}{R}: Transform this. Unveil only as a sorcery.)

Flying
Whenever another creature enters the battlefield under your control, you may have Waxing Celestial get +1/+1 until end of turn.

Create two Idol tokens, then counter target spell unless its controller pays {1} for each Idol you control. (They're artifacts with “{1}, Sacrifice this artifact: Put a +1/+1 counter on target creature. Activate only as a sorcery.”)

Exile all Inscription cards from your graveyard and all exiled Inscription cards you own. For each card exiled this way, you may inscribe it onto a creature you control. (Whenever that creature attacks, its controller may cast a copy of the inscribed card without paying its mana cost.)

Survivors you control have double strike.

At the beginning of your end step, if you cast no spells this turn, untap target creature.

At the beginning of your upkeep, each player draws a card.