For Death Strike, what does "suffered from Massive Damage" mean? If this particular dragon has ever taken 50 hp of damage or more from one attack, does the extra damage trigger? Does it have to have taken 50+ damage in one attack this encounter?

This class is strictly an upgrade over Arcane Evaluator. 3/4 BAB and no good saves and 4+ skills become full BAB, all good saves, and 6+ skills at no cost or difficulty of entry. Why is this the case?