msem-instigator

When Wealthy Merchants enters, create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Creatures you control get +0/+2 and gain hexproof until end of turn.

Whenever Weaver of Lore attacks, you may reveal your hand. Weaver of Lore gets +2/+2 until end of turn if you reveal two or more blue cards this way.

When Weaver of Mists enters, substantiate target card in your graveyard. (Put it onto the battlefield face down as a 2/2 creature. You may turn it face up and cast it at any time for its mana cost if it isn't a creature.)
Spells you cast from anywhere other than your hand cost {1} less to cast.

Vision (Whenever this or another creature you control enters, reveal the top card of your library. Then you may put that card into your graveyard.)
Whenever Weaver of the Winds envisions an instant or sorcery card, draw a card.

Counter target spell if you have more cards in your graveyard than that spell's controller.

Flying
Welkin Tern can block only creatures with flying.

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.

Enchant permanent
Whenever enchanted permanent becomes untapped, its controller gets a poison counter.

Draw two cards, then discard two cards. Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

Whenever you draw a card, target player mills two cards.
Whenever you cast a blue spell, scry 1, then you may reveal the top card of your library. If it's an instant or sorcery card, draw a card.

Return target nonland permanent to its owner's hand. Scry 1.

Draw two cards, then discard two cards if it's a combat step.
Quickdraw {U} (When a creature you control blocks or becomes blocked, you may cast this spell for {U}.)

Return target creature to its owner's hand. If you controlled that creature, draw a card.

Harness (You may tap a creature you control as you cast this spell. If you do, reduce this spell's mana cost by that creature's power.)
Return each nonland permanent your opponents control to its owner's hand.

Flash
Heretic (Whenever you cast a spell that doesn't share a color with this creature, it gets +1/+1 until end of turn.)

When Whisper Collector dies, draw a card.

When Whisper Witch enters, choose up to one target creature. That creature's controller mills four cards, then puts that creature on top of their library.

Put target instant or sorcery card from your graveyard on top of your library.
Inscribe {3}{U} ({3}{U}: Exile this card from your hand inscribed on a creature you control. Whenever that creature attacks, its controller may cast a copy of the inscribed card without paying its mana cost. Inscribe only as a sorcery.)

Whenever Whisperer of Fortunes attacks, the next card you foretell this turn costs {0} to foretell.
Whenever you cast a foretold spell, put a +1/+1 counter on Whisperer of Fortunes. It gains flying until end of turn.

Whenever an opponent casts a spell, that player mills X cards, where X is that spell's mana value.

Whenever Whitepeak Channeler deals combat damage to a creature, tap that creature. That creature doesn't untap during its controller's next untap step.

As long as you control another creature with flying, Wild Skycub has flying.

Surveil 1, then draw a card. (To surveil 1, look at the top card of your library. You may put that card into your graveyard.)
Create a tapped Treasure token.

Flying
{U}, Sacrifice Willow Spirit: Counter target spell or ability that targets you or a creature you control.