msem-instigator

Whenever Breakneck Barque becomes blocked by a creature, Breakneck Barque deals 3 damage to that creature.
Crew 3 (Tap any number of creatures you control with total power 3 or greater: This Vehicle becomes an artifact creature until end of turn.)

Choose one —
• Shredding Blizzard deals 5 damage to target creature.
• Up to three target creatures can't block this turn.

Pressure {1}{U} (You may cast this spell for its pressure cost if seven or more cards are in your graveyard.)
When Cuxuri Harbinger enters, draw a card.

Daggersworn Elite enters tapped.
Whenever Daggersworn Elite and at least two other creatures attack, you may pay {1}{B}. If you do, destroy target tapped creature.

Menace
Whenever a creature you control deals combat damage to a player, exile the top card of that player's library. They lose life equal to that card's mana value.

Double strike
Whenever an Equipment you control enters, create a 3/3 white Archon creature token with flying and attach that Equipment to that token.

This spell can't be countered.
Whenever one or more creatures with flying attack, upgrade Guided Sniper. (Give it one of the listed counters it doesn't already have.)
• +1/+1
• Reach
• Hexproof

Towering Boughs enters tapped.
{T}: Add {R} or {G}.
{3}{R}{G}: Until end of turn, Towering Boughs becomes a 6/6 red and green Treefolk creature with with trample and “Whenever this creature attacks or blocks, torment yourself.” It's still a land. (To torment yourself, lose 3 life unless you discard a card or sacrifice a nonland permanent.)

Riv's Safehouse enters tapped.
When Riv's Safehouse enters, you may mill two cards.
{T}: Add {U} or {B}.

Choose one —
• Target creature gets +1/+1 until end of turn for each creature you control.
• Creatures you control get +1/+1 until end of turn.

Adjudicate, then each player returns a creature they control that isn't enchanted to its owner's hand. (Create a white Aura enchantment token with enchant creature and “Sacrifice this token: Untap enchanted creature” attached to target creature.)

Bleed {1}{U/R} (You may cast this spell for its bleed cost if an opponent has lost life this turn.)
Copy target instant or sorcery spell. You may choose new targets for the copy.

Whenever Starlight Emissary harnesses a spell, draw a card.

Flying
When Messenger of the Heavens enters, surveil 1.
Whenever Messenger of the Heavens deals combat damage to a player, exile any number of target creatures in its pack, then return them to the battlefield under your control. (Two or more creatures you control with equal power are in a pack.)

Look at the top six cards of your library. Put one of them into your hand and the rest into your graveyard.

Reveal the top card of your library. You may put it on the bottom of your library. Target creature gets -X/-0 until end of turn, where X is that card's mana value.

Search your library for a card, reveal it, then shuffle and put that card on top.
Kindle 3—{3}{B} ({3}{B}, Exile this card from your graveyard: Create three 1/1 colorless Elemental creature tokens. Kindle only as a sorcery.)

Once each turn, when a permanent is exiled from the battlefield by a spell or ability you control, you may draw a card.

Whenever a creature is returned to its owner's hand, draw a card.
{4}{U}{U}: Return target creature to its owner's hand.

Flying
When High Spirits enters, target creature gains flying until end of turn.

{1}{B}: Target creature you control must be blocked this turn if able.
{1}{G}: Target creature you control can't be blocked by more than one creature this turn.

Whenever Tide Crasher attacks, if you control another Merfolk, tap target creature defending player controls.

[+1]: Create a white enchantment token named Intangible Virtue. It has “Creature tokens you control get +1/+1 and have vigilance.”
[–3]: Create a 4/4 white Angel creature token with flying. You gain life equal to the number of tokens you control.
[–5]: Exile all other nonland, nontoken permanents.

Target creature you control deals damage equal to its power to target creature you don't control.

When Dylso Charmer enters, if you cast it from exile, create a 2/2 white Cat creature token.
Prophecy {1}{G} (Once each turn, you may exile a card with prophecy as you reveal it. When you do, you may cast it for its prophecy cost as long as it's exiled.)