I believe any attack/summon/DoT spell in any game is an offensive spell.....
Oh, I don't know, Acrylik. Flaming sword is pretty cool if assigned to your pet. I just don't know if it gets all the bonuses it should when it's on the pet - it does certainly get the duration increase. I'm pretty sure it gets the Crit Chance improvement, but it does not seem to take advantage of avatar's Crit Strikes Skill, at least when assigned to the pet.
......if you're lucky to have access to an extra 'Blood Skeleton' spell, use it instead of 'Zombies'. In either case, it's best to max out a character's 'Charm Spell' skill - then summoned allies end up wrecking stuff left, right and center.
u sure? pet can have only 2 blood skels at a time i think