Battles can be targeted by spells and abilities that do damage, swap control and all manner of other effects
Emissary of Sunrise goes right into your B/W Clerics deck which also features Rotlung Reanimator
Sacrifice has its purposes but can also be easily navigated around by your opponent with tokens and cheap creatures
You can also supplement his vitality with Narsil, Blade of the Faithful (9R+34) or The Saga of Elendil (1R114) , although this can be risky: if one of these cards is removed when he has only one wound left, he'll die and you'll lose the game
An excellent time to strike is if your opponent has just searched for a card , such as with Enlightened Tutor , or they already have seven or more cards in hand
Even without proper setup, you can be lucky enough to play three stolen permanents on your next round and attack with this horror