I was looking over the stats of the Fire Troll from the Dragon Compendium, and I noticed something wonky...
Fiery Regeneration (Ex): The fire troll's regeneration ability draws on the energy available in areas of severe heat (110 *F or higher). Under such conditions, the fire troll's regeneration increases by 4 points to 12 points per round. If any effect that deals fire damage targets a troll, its regeneration ability increases to 20 points for 1 round. If the troll is exposed to multiple attacks
during the same round, its improved regeneration's duration remains 1 round.
Regeneration (Ex): Electricity deals normal damage to a fire troll.
Vulnerability to Cold (Ex): Trolls regenerate cold damage despite their weakness to it. If cold damage drops a fire troll to 0 or fewer hit points, it must make a Fortitude save (DC 15 + cold damage taken) or be frozen in place. The troll is helpless for 2d4 rounds. If further physical or electrical damage reduces it to -10 hit points or lower, its frozen body shatters into dozens of pieces, killing it.
Regeneration means that all damage not of a specified type is instead non-lethal damage. Non-lethal damage has no impact whatsoever on your actual hit points, and is tracked completely separately.
Cold damage CANNOT drop a fire troll to 0 or fewer hit points; it is completely impossible so long as its regeneration exists. Likewise, physical damage is incapable of dropping its hit points to -10...
So, this "vulnerability" is really anything but? Because it cannot actually activate?
(I realize they were intending to mean that this ability activated if cold damage brought its non-lethal damage total to equal or exceed its current hit points. That's not at all what the ability says, though).
