msem-instigator

Defender
Whenever Wall of Seclusion blocks a creature, that creature doesn't untap during its controller's next untap step.

Whenever Wandering Conqueror attacks, it explores. (Reveal the top card of your library. Put it into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then you may put that card in your graveyard.)
As Wandering Conqueror explores a land, you may put that card into your graveyard. Whenever you do, Wandering Conqueror deals 2 damage to target player or planeswalker.

Flash
Whenever a permanent with an Adventure you control enters, put a +1/+1 counter on Wandering Dingo.

Lifelink, haste
Wanton Cleaver has first strike as long as it's attacking.

Each instant and sorcery card in your graveyard gains agonize 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.)

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

Advance {3} (Cast this for {3} to advance it as it enters. {3}: Advance this as a sorcery.)
Whenever Wastes Scrambler advances, put your choice of a +1/+1, first strike, menace, trample, or vigilance counter on it. If {R}{W}{B} was spent to advance it, repeat this process twice.
Crew 1

Vigilance, reach
Watchful Authority can block an additional creature each combat.

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.)

Advance {5}{B}{B} (Cast this for {5}{B}{B} to advance it as it enters. {5}{B}{B}: Advance this as a sorcery.)
Whenever Well-Oiled Sniper advances, target creature gets -3/-3 until end of turn.

Wharf Lumper can't be blocked by creatures with greater power.
Whenever Wharf Lumper attacks, mill a card. If that card was an instant or sorcery, Wharf Lumper gets +3/+0 until end of turn.

When Wild Waypoint enters, create a 1/1 green Scout creature token.
{T}: Add {B}, {G}, or {U}.

When Witch's Invitation enters, you may put a -1/-1 counter on target creature.
{2}, {T}: Tap target creature with a -1/-1 counter on it.

Whenever you cast a spell, you may pay {1}. If you do, Wizened Tortle explores. (Reveal the top card of your library. Put it into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then you may put that card in your graveyard.)

Vigilance
Whenever a creature you control survives damage, it explores. (Reveal the top card of your library. Put it into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then you may put that card in your graveyard.)

[+2]: Put a -1/-1 counter on or remove a -1/-1 counter from up to one target creature.
[–1]: Draw a card, then each player sacrifices a nonland permanent.
[–10]: Destroy all nonland permanents you don't control.

Haste
When Wretched Merfolk enters, target creature can't block this turn.

At the beginning of combat on your turn, if there are seven or more loyalty counters on Ameret, they become a 5/5 Angel creature with flying and indestructible until end of turn.
[+1]: Create a 1/1 red and white Cleric creature token with lifelink and haste.
[–X]: Ameret deals X damage to any target. You gain X life.

At the beginning of your upkeep, put a loyalty counter on each planeswalker you control.
[0]: Tap target creature.
[–1]: Untap target basic land.
[–7]: Draw up to six cards.

Align X (Choose modes with total ★ less than or equal to X. You may choose modes multiple times.)
• ★ — Bloodstained Calamity deals 1 damage to each creature, player, and planeswalker.
• ★★ — Return target instant or sorcery card from your graveyard to your hand. Exile Bloodstained Calamity.
• ★★★★★ — Bloodstained Calamity deals 10 damage to any target.

You may cast target instant or sorcery card from your graveyard this turn. If that spell would be put into your graveyard, exile it instead.

Reveal cards from the top of your library until you reveal a card with a lesser mana value than the previous card, then put all cards revealed this way into your hand.

Double each number and amount of target instant or sorcery spell, activated ability, or triggered ability. Its controller may choose new targets for it. (Amounts are number words, X values, and “a” or “an” used as 1.)

Gain control of target artifact or creature until end of turn, then untap it. It gains haste until end of turn. You may spend mana as though it were mana of any type to pay the costs of its abilities this turn.

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