I think a cool thing to have would be a troop that left a burning effect on buildings. We have troops that use fiery projectiles, but none that leave burning effects. This burning effect would be similar to that of the scorcher in Boom Beach, after the unit attacks the building, it will continue to take damage for x amount of time if the unit has stopped attacking it. You could use it in army comps a similar way that wizards are used, high damage, mid-low health, and good at cleanup and disposing of certain (high housing space) castle troops and especially heros. It would also be a good addition to make it do more damage the longer it locks onto a target (like the single target inferno). A way to defend against this would be to set infernos to multi, have single target defenses close to the edge of the base, and have lots of smaller troops in your defense castle (since this unit is single target, not splash to balance it). Please tell me if I forgot to describe anything about the troop, I am kind of tired right now.

EDIT:
Suggestions:
BarbaricDrag- Name it Flamebringer