Tehras of the Silent Wing

When Tehras of the Silent Wing enters the battlefield, create a 1/1 white and black Bat
creature token with flying and lifelink.
At the beginning of your upkeep, you may pay
4 life. If you do, create a 1/1 white and black
Bat creature token with flying and lifelink for
each Bat you control.
{1}, Sacrifice a creature: You gain 1 life.