Robin, Destined Fell Vessel

Whenever Robin, Destined Fell Vessel enters the battlefield or another nontoken Human you control dies, you lose 1 life and create a 1/1 white Human creature token.
{2}: Target Human you control gains lifelink until end of turn.
At the beginning of your end step, if you have exactly 13 life, you may pay {4}{b}{b}. If you do, transform Robin.