This can only occur at Zarok's Lair; the last level. When you come in, you will be greeted by Zarok's latest minions: Fazguls. You cannot hurt them with any of your weapons, but your newly joined "Knights" will join the fray. When this happens, you will be given "Good Lightning" which keeps your Knight's health up but drains yours in the process.
Typically the strategy is to run around and holding down
to keep their health filled, but focus on 1 or 2 of them instead. This will cause you to drain your health faster as your other knights will fall and the remaining ones will have to fight more enemies. Once you drain your Life Bottles to the last one, the trophy should pop.