Servant of the Revenants

Whenever any player casts a spell, you may
pay {w}{u} and sacrifice a spirit creature.
If you do, draw a card and you gain 2 life.
{t}: creature a 1/1 spirit creature token onto
the battlefield under your controll.
....They formed from the air, conjured by the deer,
being merely a legend of the Naldeni. According to
that legend, they were once great nobles, who wanted
to conjure elementals. A mistake occured, and they
were turned into air themselfs. Now they need
a servant to lead the