msem-instigator

Whenever Professor's Assistant becomes tapped, add {R}. Until end of turn, you don't lose this mana as steps and phases end.

Erratic (When this creature dies, reveal the top four cards of your library. Put a creature card that costs less than this revealed this way onto the battlefield and the rest on the bottom of your library in any order.)
Morph {1}{G} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

As long as another creature you control is attacking, Prolific Thief can't be blocked.
Whenever Prolific Thief deals combat damage to a player, draw a card, then discard a card.

Whenever you cast a spell from exile, Promised Seeker gets +3/+3 until end of turn.
Prophecy {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.)

{1}{W}, {T}, Sacrifice Prophet of Pacifism: Prevent all damage that would be dealt to players this turn.
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.)

When Prophetic Prismite enters, draw a card.
{2}: Add one mana of any color.

Protector of the Gates can't attack unless it's equipped, enchanted, or has a card inscribed onto it.

{T}: Add one mana of any color.
{2}{G}: Provincial Herbalist gains deathtouch until end of turn.

{R}, {T}, Exert Provoker of Mountains: Create an X/X red Elemental creature token, where X is the number of spells you've cast this turn. (An exerted creature won't untap during your next untap step.)
{X}{X}{R}, {T}, Sacrifice Provoker of Mountains: Provoker of Mountains deals X damage to any target.

Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
{2}{R}, Sacrifice Prowling Beastmaster: It deals 2 damage to target player or planeswalker.

Pungent Beetle enters with a +1/+1 counter on it for each creature you controlled that died this turn.

Menace, haste

Trample, haste
Erratic (When this creature dies, reveal the top four cards of your library. Put a creature card that costs less than this revealed this way onto the battlefield and the rest on the bottom of your library in any order.)
At the beginning of the end step, sacrifice Purgator of Storms.

{G}: Exile target card from a graveyard. You gain 1 life and Purging Watchkeeper gets +1/+1 until end of turn.

Chronicle (As this enters and after your draw step, add a lore counter. Stop after III.)
[Lore I-II] Purphoros's Gemback deals 1 damage to target player or planeswalker.
[Lore III] Create a Treasure token. (It's an artifact with “{T}, Sacrifice this artifact: Add one mana of any color.”)

Whenever you cast a cryptic spell, tap up to one target nonland permanent. (Artifacts, enchantments, and modal spells are cryptic.)

Each creature you control with a +1/+1 counter on it has trample.
{1}{R}{G}: Pyresong Aspirant deals 1 damage to target creature. You may have that creature gain hexproof until end of turn.

Flying
When Pyromanticore enters, it deals X damage to target creature or planeswalker an opponent controls, where X is your devotion to red. Excess damage is dealt to that permanent's controller instead. (Each {R} in the mana costs of permanents you control counts toward your devotion to red.)

Whenever Qalami Barbarian attacks, you may discard a card. If you do, it gets +1/+2 and gains menace until end of turn.

Reach
Stampede — Whenever Qasali Quiverguard and a creature with greater power attack, untap all attacking creatures.

{1}, Sacrifice another creature: Qi Harvester gains your choice of deathtouch or indestructible until end of turn. If the sacrificed creature was in Qi Harvester's pack, draw a card. (Two or more creatures you control with equal power are in a pack.)

Flying
When Qi-Long Rainbringer enters, return up to one other target creature to its owner's hand.

Menace

Flash
When Qililia's Scavenger enters, look at the top six cards of your library. You may put a Merfolk card with lesser mana value from among them onto the battlefield. Put the rest on the bottom of your library in a random order.
Other Merfolk you control get +1/+1.

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.)