It seems the ring of fellowship + soothing collar can be helpfull in several cases for the demonologist, that imp dealing 2 damages instead of 1 everytime you roll red or wild gem on his dice. Now the other important thing is to make enough money fast so you can buy and fill more red/wild gem in the imp dice row.
Managed to beat the frozen horror level with the demonologist with
soothing collar (for the nice +1 attack on captured ennemies) + ring of fellowship (that starting imp is awesome, though you need some luck for rolling red gems) + trapper mantle (this nice additional fang for an used trap) + bottomless pouch (the +1 gold by waves may or may not have helped to fast buy more red gem)
The good bonus to capture from both the collar and the mantle helped a lot, as i captured an archdemon before the bosses waves , and with the Pet ability i had spared (and got more charges in one of the end wave bonus choice) , that captured guy killed 2 of the 3 bosses in the same turn
I was worrying things would not die fast enough for me to complete the mission before the bigger boss woke up but it worked out nicely as i had some luck with the +health bonus between waves coming when i needed for once (usually it only come when i don't need it and never come when my character is badly hurt
)
This victory managed to get me the last 2 stars i needed to unlock the demonoligst "demonifasto" for more of those usefull imps
The moonwood new mission seems to be very hard, as there are enemies you can't kill (even accidentally) (until they are transformed at night) as it will hurt your end score badly (-100 points each), very bad situation for the imps that target random enemies on screen when triggered. Managed to win this level but ended score at -7 (i had a villager captured to boost the score but so many died to my imp) so it's not even recorded in my score (as the best current one is 0
)
The boss for the sun monastery level is insane, the thing has ethereal 3 (so it does not take damage the 3 first time you attack it) and attack 9 each turn ! (and of course he's not alone so there's more damage going to you by turn) , and he's not capturable too.
Hope you have some multi-damaging attacks to get rid of his minions and hit him 3 times to make him actually vulnerable to damage. Hard to get multiple imps and enough red gems without dying first.