Inferno faction discussion.

I think both options are quite idiotic. Shooting with bones or fire. What a mess.
Succubi don't shoot with spheres. Enjoy it, Russification enthusiasts.

Is there any difference between a simple double attack?

You wouldn't argue that succubi shoot fire, would you? The bone attack is a questionable option, but such a theoretical possibility is mentioned in the description.

There is a difference. The Minotaur Guard (from "Heroes 5") will always deal two attacks to the enemy, while the Orc Veteran (from King's Bounty) will only do so if there is a retaliatory attack! If the first happens quite often, I've only seen the second in King's Bounty.