If obtained by exchanging an Unfocused reward enhancer with Wythien, the enhancer will have only 1 charge.
You do not need to actually be on his Special challenge to be revived. It will work when fighting the monsters associated with the challenge. This includes:
- Giant mole
- Kalphite Queen
- King and Queen black dragon
- Dagannoth Prime, Rex, and Supreme
- Commander Zilyana, General Graardor, Kree'arra, and K'ril Tsutsaroth