As i'm farming kills on these for fun, I notice there could be a few things done to make this a less tedious thing,
Cerb
Alow it to respawn, at a 30 second rate, leaving and coming back gets a bit lame.
Kraken
Alow it to respawn, at 30 second rate, leaving and coming back gets a bit lame :)
zulrah
add a portal to the inside of the fight, when you click on it it'll return you to the area.