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.

(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.)