Rathma, the Necromancer

Whenever Rathma, the Necromancer enters the battlefield, exile a creature from your graveyard
and put a Black 1/1 Skeleton token onto the battlefield under your control.
{b}{t}, exile a creature from your graveyard and
put a Black 1/1 Skeleton token onto the battlefield under your control.
At the start of your turn, if you do not control a creature named Rathma, the Necromancer,
destroy all skeleton tokens you control.