Spirit Bonds

Oracle Text

Whenever a nontoken creature enters the battlefield under your control, you may pay W. If you do, create a 1/1 white Spirit creature token with flying.

1W, Sacrifice a Spirit: Target non-Spirit creature gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Card Rulings

7/18/2014 You decide whether to pay as the triggered ability resolves. You may only pay and create a Spirit token once per nontoken creature.
7/18/2014 You can sacrifice any Spirit to activate the last ability, not just a Spirit token created by Spirit Bonds.