msem-instigator

Put a +1/+1 counter on target creature.
Inscribe {2}{W} ({2}{W}: 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.)

Enchant player
At the beginning of enchanted player's draw step, they draw an additional card.
At the beginning of enchanted player's end step, that player discards all but one card in their hand.

Target creature gets -2/-2 until end of turn. When that creature dies this turn, its controller loses 2 life or gets a poison counter.

Flash
Whenever Thundermane Fox enters or attacks, target creature you control gains double strike until end of turn.

Siphon (Each -1/-1 counter you put on your creatures up to their remaining toughness while casting this pays for {1}.)
Choose up to X, where X is the amount of mana spent to cast this spell —
• Target creature gets -3/-3 until end of turn.
• Surveil 2.
• Create a 1/1 black Bat creature token with flying and “This creature can't block.”

When this creature enters, return a creature you control to its owner's hand.
{2}{U}: This creature gets +2/-2 until end of turn.

Target creature gets -2/-0 until end of turn. If that creature is tapped, draw a card.

Reach
As long as you control an artifact or an enchantment, Heron's Grace Patrol gets +1/+1 and has vigilance.
{2}{G}{W}, {T}: Mill three cards. You may return a permanent card milled this way to your hand.

Puzzlebox (Begin the game with this and another card you own from outside the game in the command zone, locked. That card is face down until you unlock this.)
{2}, Discard your hand: Unlock Traitor's Gambit. If the revealed card is red, put it into your hand. Otherwise, put it on top of your library.

Whenever Supplanter of Realities attacks, proliferate. (You choose any number of permanents and/or players with counters on them, then give each another kind of a counter already there.)
Sacrifice another permanent: Supplanter of Realities gains indestructible until end of turn. Tap it.

Creatures you control get +1/+0 and gain haste until end of turn.

{T}: Add {C}.
{1}, {T}: Add one mana of any color.
{2}, {T}, Sacrifice Great Beyond: Draw a card.

Wither (This deals damage to creatures in the form of -1/-1 counters.)
Whenever Barrow Banshee deals combat damage to an opponent, that player discards a card at random.

Exile target nonland permanent.

Double strike
Engage (This creature must be blocked each combat if able.)
{1}{R}: Balanced Blade gets +1/+0 until end of turn.

When Hirukari's Immortal dies, if it didn't enter this turn, create a token that's a copy of it, except it has no mana cost.

Target creature you control gets +1/+1 and gains indestructible until end of turn.
Fabled {3}{W}{W} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that creature.)

Untap up to two permanents you control during each other player's untap step.

Prowess
When Snowline Ascetic enters, you may put target instant or sorcery card from your graveyard on top of your library.

When Hellion Devastator enters, destroy up to one target nonland permanent with mana value 3 or less.
Cycling {2} ({2}, Discard this card: Draw a card.)

Attacking creatures have winnow. (Damage dealt to a creature with winnow also causes its controller to lose that much life.)

When Rotting Sunseeker dies, return target creature card with power 2 or less from your graveyard to your hand.

Tap an untapped creature you control: Put a charge counter on Channel the Spirits.
Remove nine charge counters from Channel the Spirits and sacrifice it: Creatures you control get +3/+3 and gain trample until end of turn. Activate only as a sorcery.

Frondpond Prankster can't be blocked.
Whenever Frondpond Prankster enters or deals combat damage to a player, target player reveals their hand, then you choose any number of nonland cards from it. That player puts those cards on the bottom of their library in a random order, then draws that many cards.

Destroy target artifact or enchantment. If you controlled that artifact or enchantment, draw two cards.