A skill tree of 4 parts will be excellent
•spells
•servants
•duelists
•affinity(shadow only)
Starting with the shadow sneak spell I would like a skill that increases the amount of fuel obtained from killing bunnies or monkeys increased, increased radius for the skill will be good too as well as increasing the panicking duration for other mobs. Now the shadow prison deserves as well smth like more radius, but increased prison time will be quite cheesy so I don't recommend it,moreover I see the ability of the prison to cancel first,second attacks of a mob is more suitable.
Now for the servants ability to work faster will be neat, as well as an increase to their range and their lifespan(I was going to recommend the ability to mine werepig walls and others but that would be bit off but also good if it gets added)
As for the duelists a skill to make them receive less damage when not getting hit for long an ability to dodge first and perhaps a second hit from a mob without receiving damag a shadow barrage skill will be good(shadows do a slash attack after 6 successful hits)
Finally for the shadow affinity shadows from the nightmare fissures will be passive to maxwell as well as normal nightmares will agro if attacked.
Extra thing which I have a big doubt if its added a shadow sailor or a shadow farmer.
Now I know some stuff might not be balanced but am always happy about ur opinoins