msem-instigator

Counter target spell, activated ability, or triggered ability unless its controller pays {X}. (Mana abilities can't be targeted.)

Hexproof
When Elusive Devout enters, choose one —
• Put a +1/+1 counter on Elusive Devout.
• Create a colorless artifact token named Lotus Petal with “{T}, Sacrifice this artifact: Add one mana of any color.”

If a permanent would deal damage to Elusive Fatecrafter, instead prevent that damage and exchange control of Elusive Fatecrafter and that permanent.

Flash
{U}, Put Elusive Hunter into its owner's library second from the top: Counter up to one target spell unless its controller pays {2}.

Flash
When Elusive Illusionist enters, target attacking creature gets -2/-0 until end of turn.

{1}{U}: Exile Elusive Monkey. Return it to the battlefield under its owner's control at the beginning of the next end step.

Foresight — Whenever you draw your second card each turn, Elusive Sage can't be blocked this turn.

{1}: Look at the top card of your library.
{G}, {T}, Mill a card: Untap another target creature.

Enchant artifact or creature
When Embed enters, tap enchanted permanent.
Enchanted permanent doesn't untap during its controller's untap step.

Flying
Other Elementals you control get +0/+1 and have flying.

Target player shuffles up to three target cards from their graveyard into their library.
Acquiesce (If you cast this spell from your hand, exile it as it resolves. When one or more creatures you control deal combat damage to an opponent, you may cast this card from exile without paying its mana cost.)

Flash
When Emissary of Dark Tides enters, you may return target noncreature spell or tapped creature to its owner's hand.

Whenever you cast a spell, if you cast it for an alternative cost or cast it from anywhere other than your hand, create two 1/1 blue Elemental creature tokens with flying. (Reconstruct and rhapsody are alternative costs, hybrid costs are not.)

Draw four cards.
Metamorph {3}{U}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up and cast it at any time for its metamorph cost.)

Return all nonland permanents to their owners' hands.

As an additional cost to cast this spell, you may tap
any number of untapped Angels and/or Nephilim you control. This spell costs {1} less to cast for each creature tapped this way.
Flying, vigilance
When Empyrean Scholar enters, each creature tapped to pay its additional cost becomes a 4/4 Angel creature with flying and vigilance. (This effect lasts indefinitely.)

Create a token that's a copy of target nonland permanent you control with mana value X.
Flashback—{U}{U}, Exile cards from your graveyard with exactly X card types among them. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Counter target creature spell. You may cast a copy of that spell. (You still pay its costs. The copy becomes a token.)

Reprise {4}{U} (As you cast an instant or sorcery spell, you may exile one card with reprise from your graveyard and pay its reprise cost. If you do, add its effects to that spell.)
Target player mills a card. Create X tapped 2/2 black Zombie Pirate creature tokens, where X is the total number of cards milled by this spell.

Copy target instant or sorcery spell. You may choose new targets for the copy.

Each player can't cast more than one spell each turn.
You may cast spells from your hand without paying their mana costs.

{U}, Put a travel counter on Endless Discoveries: Draw a card. This ability costs {1} more to activate for each travel counter on Endless Discoveries.
{3}{U}{U}, Sacrifice Endless Discoveries: Return target instant or sorcery card with mana value less than or equal to the number of travel counters on Endless Discoveries from your graveyard to your hand.

Whenever you cast a noncreature spell, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)

Draw a card for each creature you control.
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.)

Any number of target players mill twice X cards, where X is the number of artifacts and enchantments you control. Then you may cast a nonland card with mana value X or less from a graveyard without paying its mana cost. You can't cast more spells this turn.