I've seen Spark up twice recently, on todays occasion I had been clearing Wisps along the hill that runs alongside the lake. There are three or four wisps that path along the top and sides of this hill and as a result of clearing them he popped so I believe that one of these wisps is his Placeholder. This would tally with an earlier sighting a month or so ago where again I spotted him along the top of this hill.
Best way to describe the location is if you stand at the stone entrance to what will become Surefall Glade and look to the right of the pathway leading from it, the ridge is the hill to the right of that path, runs parallel with the lake.
In addition to the three items already listed as his drops, he also drops Fine Wisp Essence and Cracked Lightstone
Edited, Jan 18th 2011 2:57pm by TorrinTook

Archaic Plate Gauntlets
Band of Luminescence
Circlet of Living Light