Ran into an issue with the TD script on this one because my Energized Manafiend solo'd the entire encounter and my leveling pet never swapped in. Since the Energized Manafiend has Surge of Power it cast it as soon as enemy #3 came in.
I added a line (2nd line) which should cause you to swap in your level pet if your Manafiend is still alive and enemy #3 comes in:
Erris' pets have two movesets just as playable pets do, and Bones can have either negligible Death and Decay or Call Darkness, which is devastating to dragons. I don't say it would be impossible to bring Bones' health to 0 (requires a check for dragon racial), but the leveling pets would still deal with the undead round. I suppose a higher level carry would suffice ^^