You might not want to play them on Lunatic then. On Chapter 17 they come with Poison Strike AND Grisly Wound, which means 40% lost HP if you can't kill him on his turn and 20% lost on your turn. The great thing is though you can capture them and use them on your team. There is one in the northern part of the map that has Movement +1 on top of PS, GW, and LT.
On Chapter 25 they come with the enemy exclusive skill Inevitable End which enables unlimited stacking for debuffs (Hint: Get Shurikenbreaker ASAP)
Yea, after Conquest you'll end up with a burning hatred for Ninjas.