msem-instigator

Mark (Whenever this creature attacks, mark target creature until end of turn.)
Whenever Backalley Silencer deals combat damage to a player, destroy target marked creature.

(As an Encounter enters, choose an opponent to protect it. You and others can attack it. When defense counters are removed, create a 0/0 Army token if you don't control one, then put that many +1/+1 counters on a Army you control.)
When Crisis in Danaj enters, return target creature an opponent controls to its owner's hand.

Whenever you cast a noncreature spell, Novice Pyromancer deals 1 damage to target player or planeswalker.

When Guardian of Lost Truths enters, if a library has twenty or fewer cards left in it, draw two cards. Otherwise, target player mills five cards.

Menace
Landfall — Whenever a land you control enters, create two 1/1 red and white Warrior creature tokens with haste. Exile them at the beginning of the next end step.

Choose land or nonland. Reveal cards from the top of your library until you reveal a card of the chosen kind. Put that card into your hand and the rest on the bottom of your library in a random order.

Whenever another creature you control enters, Flightpath Trainee gains flying until end of turn.

Alpha (You may have this creature enter with a +1/+1 counter on it. If you do, it becomes alpha and can only attack alone.)
When Xiejuan, the Regal Beast becomes alpha, draw a card for each other creature you control.

(Activate each ability only once as a sorcery. You gain the realm's favor after activating them all.)
{W}: Put a first strike counter on target creature.
{1}{W}: Invigorate 2. (Choose a creature with the least power among creatures you control and put two +1/+1 counters on it.)
{2}{W}: Create two 1/1 white Soldier creature tokens.
Creatures you control with counters on them have flying and lifelink.

When Gleeful Deviser enters, create a 1/1 colorless Construct artifact creature token.

When Escaped Ooze enters, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)
{3}{G}: Put a +1/+1 counter on Escaped Ooze.

Flash
Flying
Sacrifice Vengeful Messenger: Counter target noncreature spell unless its controller pays {2}.

Flash
Enchant creature
Whenever enchanted creature deals combat damage, put that many +1/+1 counters on it.
When enchanted creature leaves the battlefield, distribute X +1/+1 counters among any number of target creatures you control, where X is the number of +1/+1 counters it had on it.

Whenever you draw a card, put a loyalty counter on Tara, Duneblessed.
[–1]: Create a 1/1 white Soldier creature token. Investigate.
[–2]: If target artifact or creature is tapped, exile it. Otherwise, tap it and put a stun counter on it.
[–10]: Choose up to one creature. Destroy the rest.

Flash
When Brutalizer Gear enters, attach it to target creature you control.
Enchanted creature gets +3/+3 and has trample.
Equip {5} ({5}: Attach to target creature you control. Equip only as a sorcery.)

Whenever Illumination Savant attacks, harmonize. (Trigger up to one harmony of a permanent you control.)
Harmony — Put a +1/+1 counter on each artifact creature and enchantment creature you control.

Choose one —
• Exile target player's graveyard.
• Target player sacrifices a creature.

Target creature gets +1/+0 until end of turn. Add {R}.

At the beginning of your end step, aetherize target permanent you control. (To aetherize, create a token that's a copy of it, then exile that token.)

When Fretport Warden enters, scry 2.

Double strike (This creature deals both first-strike and regular combat damage.)
If three or more creatures are attacking you, you may cast Timely Commander as though it had flash.

Protection from sorceries
Whenever Magdel, Caller of Souls attacks, create a 1/1 white Spirit creature token with flying that's tapped and attacking for each storied permanent you control. Exile the tokens at end of combat. (Enchantments and legendary permanents are storied.)

Reach
If a creature is attacking you and you control a Centaur, you may cast Qilan Archer without paying its mana cost and as though it had flash.

Encourage ({T}: Another target creature you control gets +1/+1 until end of turn. Encourage only as a sorcery.)
Whenever Paladin's Attendant encourages a creature, that creature gains first strike until end of turn.

Target creature gains deathtouch until end of turn. If that creature is an Insect, it gains first strike until end of turn.