"Stay in the light. I don't know what lurks in those shadows, and I'd like to keep it that way."

Ollenbock Escort

Vigilance
Sacrifice this creature: Target creature you control with a +1/+1 counter on it gains lifelink and indestructible until end of turn.

Innistrad: Double Feature

Innistrad: Crimson Vow

The creature having a +1/+1 counter on it is part of the targeting requirement of Ollenbock Escort's ability. After the ability has resolved, the creature won't lose lifelink or indestructible if the counter goes away.