I can answer your question about Ninja but not the drone.
Using the normal training upgrade the Oni gets Circle of Fire which is an immobilse when you get the lvl 32 enlighten he gets Char which is a hold.
You can get the Oni to open with a cone of fire with 99% efficiency by using range. Whatever range hes at when you hit the attack my target button bases what he does. So if hes medium to close he will always use cone of fire if its available. Further away he tends to blast or immobilise.
The poison trap tends to stop a mob for a few seconds. unslotted it isnt very good. The corrupter poison trap is very good at toogle dropping. Dont know if the mm trap is the same.
I still feel like a noob a lot of the time... These questions are part of that!
Firstly, the Oni can slot hold enhancements but not immobilise enhancements - he starts every attack with immobilize, so I wouldn't mind slotting that, but I don't think he has a hold at all...
Secondly, is there a good way to use seeker drones? They seem like they could be useful, but whenever I meet anything tough, they always seem to veer off and hit a minion away from the main threat!
If anyone has any tips, I'd love to hear them, also how good is poison trap, as I haven't picked that yet?