Tetra Spiritdancer

Whenever an Aura enters the battlefield under
your control, create a 0/1 white and blue Spirit
creature token with flying, then create a token
that's a copy of that Aura and attach it to target
Spirit creature token you control.
Whenever a Spirit you control dies, if an Aura
you controlled was attached to it, draw a card.
When Tetra Spiritdancer leaves the battlefield,
exile all Aura tokens you control.