From WoWWiki

Enfeeble is a skill used by Prince Malchezaar in Karazhan.

Prince Malchezaar Enfeebles 5 random players, excluding the current target. Enfeeble reduces their max hit points to 1, and healing effects and health regen to 0% for about 7 seconds. Healing enfeebled targets has no effect. Enfeebled players must stay 30+ yards away from Malchezaar and watch out for Infernals. After the Enfeeble is up, players return to their previous health.