Rulings

• If a spell or activated ability has a cost that requires a player to pay life (as Griselbrand’s activated ability does) or sacrifice a creature (as Fling does), that spell or ability can’t be cast or activated.2012-05-01
• Other things may still cause players to pay life or sacrifice creatures, such as a resolving spell or ability.2012-05-01
• Angel of Jubilation’s last ability doesn’t look for specific words on other cards. Rather, it stops players from taking specific actions. For example, you couldn’t activate an ability with an activation of cost of “Sacrifice an artifact:” by sacrificing an artifact creature (although you could sacrifice a noncreature artifact).2012-05-01