msem-instigator

Creatures have “Whenever this creature attacks or blocks, it fights another target creature.”

Choose one —
• Counter target spell unless its controller pays {2}.
• Draw a card.

Siphon (Each -1/-1 counter you put on your creatures up to their remaining toughness while casting this pays for {1}.)
Draw three cards.

Target creature gets +5/+5 until end of turn.
Fabled {4}{G} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that creature.)

Whenever Herald of Purity is dealt damage, it deals that much damage to any target.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Golden age (If you cast an instant or sorcery spell, activated a nonmana ability, and attacked this turn, enter a renaissance for this game.)
{1}{R}: Mieng gains flying until end of turn.
Whenever Mieng attacks, create a 4/4 red Dragon creature token with flying that's tapped and attacking. Exile that token at end of combat unless you're in a renaissance.

Whenever a creature attacks you or a planeswalker you control, Pitfall Pangolin gets +1/+0 until end of turn.

Quan Li, Dusk Operative enters with your choice of a deathtouch or +1/+1 counter on her.
Once each turn, whenever a creature in Quan Li's pack dies, create a 1/1 colorless Spirit creature token. (Two or more creatures you control with equal power are in a pack.)

As Sunlit Highland enters, you may pay 2 life. If you don't, Sunlit Highland enters tapped.
{T}, Sacrifice Sunlit Highland: Search your library for a Mountain or Plains card, put it onto the battlefield, then shuffle.

Whenever Inkwell Daggers enters or attacks, proliferate. (Choose any number of permanents and/or players with counters on them, then give each another counter of each kind already there.)

Somberwald Rider can't be blocked by creatures with power 2 or less.
{2}{G}: Transform Somberwald Rider. Activate only if it's attacking.

Flying, trample
Whenever Skali, the Last Sunfeather attacks, abound. If a creature spell is cast this way, you may have that creature enter tapped and attacking. (To abound, you may cast a spell that costs less than this from your hand without paying its mana cost.)

Stampede — Whenever Knotvine Preserver and a creature with greater power attack, until end of turn, attacking creatures you control gain “When this creature dies, return it to its owner's hand.”

{1}{B}, Sacrifice another creature, Discard two cards: Search your library for a card, put that card into your hand, then shuffle.

Flash
When Hidden Sprout enters, put a +1/+1 counter on target creature.

Reveal cards from the top of your library until you reveal a card with a lesser mana value than the previous card, then put all cards revealed this way into your hand.

Flying
Whenever you cycle Seraph of the Stage or it attacks, audition for white. (Create a 1/1 Construct Actor creature token, a Scout Role giving 2/3 and vigilance, or a Cleric Role giving 2/2 and lifelink. Roles replace older ones.)
Basic landcycling {1}{W} ({1}{W}, Discard this card: Search your library for a basic land card, reveal it, and put it into your hand, then shuffle.)

Target player creates two 1/1 white Spirit creature tokens with flying.
Fabled {3}{W}{W} (Then if you cast this for its fabled cost, put it onto the battlefield transformed attached to that player.)

Return target creature to its owner's hand. You may shuffle up to four target cards from your graveyard into your library.

Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
{2}, Sacrifice a creature: Put a +1/+1 counter on Desert Marauder.

Lifelink
Frostguard Sentry has flying as long as it has a +1/+1 counter on it.

This spell costs {X} less to cast, where X is the greatest power among creatures you control.
{1}: Target creature in Indomitable Anchorite's pack gains indestructible until end of turn. (Two or more creatures you control with equal power are in a pack.)

Whenever a storied permanent you control enters, each opponent loses 2 life. (Enchantments and legendary permanents are storied.)

{T}: Add {C}. Put a fusion counter on Eternal Reactor.
{2}, {T}: Add {C} for each fusion counter on Eternal Reactor.

Flash
Flying
Romantic Wisp can block only creatures with flying.