Engaging him starts the script and fight.
After some 10-15% health loss he runs from his spawn spot near Dranik's Scar towards the back-tunnels leading up to the The Keeper (the monk on top of the bridge in the center of the zone).
While running he does not seem to be able to take damage. He runs fast, so keep up. He stops after a few hundred feet and seem to call help from one or two Dragorn Flunkies, who rushes in to help.
At this point you can damage him again. At level 85 I just ignored the flunkies and kept meleeing on Jekisia. After another 10-15% health loss this repeats, i.e. he runs a few hundred more feet and calls more flunkies.
When he reached the Keeper he was down to 15-20% and I could finish him off, and subsequently kill off the train of flunkies I had on my back (about 8-10 of them).
Since this was just a curious try on a mob I never saw before, just passing by and found him on track, I was not prepared for a script. Thus, this explanation may need a little more detail and accuracy.