The Health Steal challenge in the Musphelheim crucible is one of the more fun of the challenges. Your health is going to continuously drop while in combat. The only way to stop it is to damage enemies, which will steal their health and restore your own.
The main trick to this one is to kill the enemies as quickly as possible. The faster you damage enemies, the easier the challenge becomes since you do not have to worry about your health falling all the way to zero.
There isn’t too much challenge to this one so you shouldn’t be under too much stress trying to complete it. If any aspect of it is troublesome, check out the video guide below for the complete guide.