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Negate Healing
Cleric Utility

Special: You can only use one Channel Divinity power per encounter.

Trigger: An enemy within 5 squares of you regains hit points or gains temporary hit points.

Target: The triggering enemy

Effect: The target doesn't regain hit points or gain the temporary hit points.

Negate healing is a cleric channel divinity power introduced in Unearthed Arcana: Ignorance is Blessed. It is meant as a substitute for divine fortune. As an Unearthed Arcana resource, it might not necessarily be canon, and may need to be discussed by the DM first. [Dr398:UA]

This power has not been rated in the character optimization guides, but it's not a useful power because it is situational to the rare enemy that heals themself.