msem-instigator

Flying, deathtouch, lifelink
Ride {1}{B} ({1}{B}: Transform this and attach it to target creature you control without a Steed. Ride only as a sorcery.)
You may activate Bonescourge Kazadrak's ride ability from your graveyard by sacrificing a creature in addition to paying its other costs.

When Ema, the Traveler enters, reveal the top five cards of your library. Put any number of legendary cards revealed this way into your hand and the rest on the bottom of your library in any order.
{2}{B}: Another target legendary permanent gains indestructible until end of turn.

Whenever you activate a nonmana ability of a permanent during your turn, you may choose one that hasn't been chosen yet this turn —
• That permanent becomes a 3/3 Dragon creature with flying in addition to its other types until end of turn.
• Each opponent discards a card and loses 2 life.
• Copy that ability. You may choose new targets for the copy.

Trample, haste
Skullbriar gets +1/+1 for each creature card in all graveyards.
{T}: Add {B} or {G}.
Skullbriar, Death's Mockery remains transformed as it moves to any zone other than a player's hand or library.

(Transform this if it's not attached to a creature.)
Enchant creature you control
The Scourgebone Pact's rider gets +2/+1, has flying, lifelink and deathtouch, and can't dismount. (This still transforms into a creature if its rider leaves the battlefield.)

Wesgoth Cemetery enters tapped.
Whenever a nontoken creature dies, put a corpse counter on Wesgoth Cemetery.
{T}: Add {B} or {G}. If there are thirteen or more corpse counters on Wesgoth Cemetery, remove those counters, transform it, then untap it.
Wesgoth Cemetery can be your commander.