Gaster, scientist of shadow

Flash
When Gaster, scientist of shadow enters the battle field, sacrifice X creatures, then draw X cards.
At the beginning of your upkeep, you may pay {1}{u}{b}. If you do, create a 2/2 colourless Gaster Blaster artifact creature token with flying.
{1}{u}{t}, pay 1 life: surveil 1, then draw 1.