Here i will list all the bosses that i find are missing on the Spawn Predictor tool.
The Pale Count
Then there are those related to raids such as:
Grand Mother Foulscale
Cublarc the Plunderer
Zulazza the Corruptor
Chizzoron the Distorter
(All of the four pirate bosses even if don't know if that' can be predicted... but)
I'll be adding more if they pop up :D
Cannot be predicted as they can be killed with Killing in name...
I have add some of them, rest will follow later.