Re: need some help with understanding "undefended damage"
My guess is that it is related to role-play or some such card-games (like Pokémon). It probably means that the creature in question attacks (after rolling dice or whatever) and its characteristics impoly that the opposing creature will be unable to defent itself from the attack.
That said, I'm still thinking of a proper way to express what the OP wnats to state. None of the options sound well to me.
Please be aware that I'm neither a native English speaker nor a teacher.