This is a simple method I came up with for evaluating the power of mobs. A mob's power level is (HP*DPS*√BPS) where HP is health combined with armor (so if a mob has 20 health but 80% armor, that's 100 HP), DPS is damage per second (if a mob has more than one attack, it's the attack with the highest DPS, 0 damage counts as 0.1) and √BPS is the square root of the mob's speed in blocks per second.
Example: Steve's Power LevelEdit
Steve has 20 health. He can punch around 4 times a second for 1 damage each, so that's 4 DPS. He can move at 5.6 blocks per second when he's sprinting, and the square root of that is around 2.37. With the formula we have 20*4*2.37, which is 189.3. So Steve's power level is 189.3 with no armor.