Toughness

Definition
While in fever, bosses gain a hidden toughness gauge, which depletes with every attack dealt to it. Once the gauge is fully depleted, the boss enters the downed state. The higher a boss's toughness, the more difficult it is to down it. Skills and power flips deplete toughness by a varying amount, whereas direct attacks deplete toughness by one for every hit.

Formula
Toughness is only applicable to bosses in general; other mobs cannot be downed. The formula for toughness is given by TP = floor(tp_basic_value * tp_multiplier * tp_scaling_boss_battle),

depends only on the boss' level, and is given as follows. Combining this information, we find * Minimin is not considered a boss.

Skills and Power Flips
Toughness depletion due to skills and power flips are given as follows.

[To be compiled.]