msem-instigator

When Blossom-Sower Witch enters, investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)
Whenever you sacrifice a permanent, you gain 1 life.

Deathtouch
Whenever Ghul of Forgotten Pasts dies, you may exile it. If you do, return target creature card from a graveyard to the battlefield under your control. You gain life equal to that card's mana value.

{T}: Exile two target creature and/or land cards from a graveyard. Create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)
{B}{G}, Sacrifice two Vials: Sacrifice Leticia Petrine, then return her to the battlefield transformed under her owner's control.

Reach
Whenever another creature you control dies, surveil 1.
{T}, Sacrifice a non-Spider creature: Create a 1/2 green Spider creature with reach.

{T}, Sacrifice another creature: Return target creature card with mana value equal to 1 plus the sacrificed creature's mana value from your graveyard to the battlefield. Activate only as a sorcery.

{T}, Pay 1 life: Add one mana of any color.

Double strike
Motley — As long as there are five or more names among nonland permanents you control, Champion of Blades has vigilance, trample, and haste.

When Commander of the Cavalry enters, you may search your library for a creature card with ride, reveal it, and put it into your hand. If you do, shuffle.
{X}, {T}: Put a creature card with ride and mana value X or less from your hand onto the battlefield transformed and attached to another target creature you control without a Steed attached to it.

Ward {1}
Other Scouts you control get +1/+1.
Whenever three or more Scouts you control attack, draw a card.

Shu Qin enters with your choice of a flying or +1/+1 counter on him.
At the beginning of your upkeep, choose a creature in Shu Qin's pack. He gains that creature's abilities until end of turn. (Two or more creatures you control with equal power are in a pack.)

{1}, {T}: Tap target creature. Rising Sun Ascetic deals 1 damage to that creature's controller.

Whenever a land you control enters, untap Ageless Wanderer.
{1}, {T}: Add one mana of any color.

{2/R}{2/R}: Churning Rough-Roller gets +1/+1 and gains double strike until end of turn.

{T}: Add {C}.
{T}, Pay 1 life: Add one mana of any color.

Reclusive Copse enters tapped.
{T}: Add {B} or {G}.
{1}{B}{G}: Until end of turn, Reclusive Copse becomes an Insect creature with deathtouch in addition to its other types.
Scavenge {B}{G}

When Restless Explorer enters, search your library for a land card, reveal it, put it into your hand, then shuffle.

As The Mistake enters, choose a card name.
Activated abilities of sources with the chosen name can't be activated unless they're mana abilities.
Unveil {5} ({5}: Transform this. Unveil only as a sorcery.)

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Weedy Whackers attacks, create a 1/1 green Insect creature token that's tapped and attacking.

When Almgrove Librarian enters, look at the top card of each of your libraries, then for each of those cards, put it on the top or bottom of one of your libraries.

(Transcend as a sorcery to gain that type and a +1/+1 counter.)
Flying
{1}{W}: Demigod — Return up to one target creature card with mana value 2 or less from your graveyard to the battlefield.
{3}{W}: God — Put a +1/+1 counter on each creature you control with the least power among creatures you control.

Permanents entering the battlefield don't cause abilities of permanents to trigger.

When Confident Traveler dies, create a 1/1 white Human creature token. If Confident Traveler was sacrificed, create two of those tokens instead.

When Confining Priest enters, exile another target creature with power 4 or less an opponent controls until Confining Priest leaves the battlefield. (That creature returns under its owner's control.)

Flying
Other Spirits you control get +1/+1.
Whenever a Spirit you control attacks, you gain 1 life.

Sacrifice Devoted Dancer: Target creature gains indestructible until end of turn. If it's your turn, shuffle Devoted Dancer into its owner's library.