There are lots of people saying different things about the effectiveness of killing Immolatus so I thought I would add my data point: I camped this on 3 different servers for about two weeks, killing any rats around the area, with no luck, and this morning at around 8am EST I found one. I did two things differently: I battled a tainted rat that was within the vale (normally I only see them at the edges) and a few minutes later I killed Immolatus. Spawned immediately after.
There are lots of people saying different things about the effectiveness of killing Immolatus so I thought I would add my data point: I camped this on 3 different servers for about two weeks, killing any rats around the area, with no luck, and this morning at around 8am EST I found one. I did two things differently: I battled a tainted rat that was within the vale (normally I only see them at the edges) and a few minutes later I killed Immolatus. Spawned immediately after.