I took a look for him and found him just west of the bandit camp in the water, conned yellow to my 22 Druid, but I took the chance. He resisted root a couple times but with stinking swarm and some careless lightning I managed to get him.
And he dropped Broons Eye first time. I also noticed that Droon jogged down to his spot from up river, so it does look like killing him spawns Droon