msem-instigator

Whenever you cast a creature spell or create a creature token, you may exile target creature you control. Return it to the battlefield under its owner's control at the beginning of the next end step.

Enchant creature
When Feline Furor enters, it deals 2 damage to enchanted creature.
Enchanted creature gets +2/+0 and has menace.

Whenever a player casts a spell from their hand, they reveal the top card of their library. If it's a nonland card with a mana value less than that spell's, they may cast it without paying its mana cost. Otherwise, they put it on the bottom of their library.
{2}{U}: Scry 1.

You have hexproof.
Adorned — Youthful Savior has hexproof as long as it's equipped and/or enchanted.

Unending Slime enters with X +1/+1 counters on it.
{2}{G}{G}{G}: Return Unending Slime from your graveyard to your hand.

{T}: Add {C}.
{3}, {T}, Sacrifice Abandoned Sanctuary: Search your library for a land card with a basic land type and put it onto the battlefield tapped, then shuffle.

Enchant creature
Enchanted creature gets +2/+2 and has vigilance.
Sacrifice Spirit Guidance: Exile enchanted creature, then return it to the battlefield under its owner's control.

{T}: Add {C}.
{1}, {T}: Add {U}{R}.

Choose target creature you don't control. When that creature dies this turn, draw a card. Target creature you control fights that creature.

Flash
When Prismatic Champion enters, create a white Aura enchantment token named Sunward attached to target creature. The token has enchant creature and “Enchanted creature has protection from creatures.”

Enchant creature
When Bramble Armor enters, put a +1/+1 counter on enchanted creature.
{G}, Sacrifice Bramble Armor: Enchanted creature gains indestructible end of turn. Tap it.

Whenever you discard a card, tap up to one target creature.

{T}: Add {C}.
Ascend—Tap ten untapped permanents you control. (Tap ten untapped permanents you control: Exile this land, then return it to the battlefield transformed. Ascend only as a sorcery.)

When Zhedina Envoys leaves the battlefield, create two 1/1 Scout creature tokens that are all colors.

Counter target spell.
Spell mastery — If there are two or more instant and/or sorcery cards in your graveyard, that spell's controller reveals their hand. You may exile a nonland card from that player's hand. If you do, that player draws a card.

Primal {5}{W}{B} (During your turn, you may cast this spell for {5}{W}{B} instead of playing a land.)
Destroy all creatures. If this spell was cast for its primal cost, for each player, put up to one creature card from that player's graveyard onto the battlefield under your control.

Enchant creature (Target a creature as you cast this. This card enters attached to that creature.)
Enchanted creature gets -2/-2.
Whenever enchanted creature blocks, its controller loses 2 life.

Flash
Reach
Experience (Whenever this creature attacks, if it has fewer than three +1/+1 counters on it, put a +1/+1 counter on it.)

Once each turn, you may reveal a creature card as you draw it. Whenever you do, create a 1/1 green and blue Bird creature token with flying and “{T}: Add one mana of any color.”
Whenever three or more creatures you control deal combat damage to a player, untap each creature you control.

Flying
When Rushwater Hunter enters, you may return target creature to its owner's hand.

Defender
{T}: Another target creature gains haste until end of turn.

When River Miscreants enters, target creature you control can't be blocked this turn.
{2}{U}: Return River Miscreants to its owner's hand. Activate only as a sorcery.

As long as Champion of Ideals has one or more +1/+1 counters on it, it's an Angel with base power and toughness 4/4, flying, vigilance, and lifelink.
{3}{G}: Judge target creature you control. Activate only as a sorcery. (Honor it by putting a +1/+1 counter on it or condemn it by sacrificing it to draw a card.)

When Skittering Atrocity enters, up to one target creature gets -X/-X until end of turn, where X is the number of Horrors you control.

Whenever you cast a noncreature spell, Sara, Entelan Elementalist gets +X/+0 until end of turn, where X is Sara's power. It deals 1 damage to each creature you don't control.