Talk:Kog'Maw/@comment-178.59.120.223-20111026124333/@comment-201.22.211.8-20111102025504

A common myth is that you shoudn't get percent and flat penetration at the same time. They may not be 100% cost-efficient, but become very deadly together when even through one reduces the efficiency of another. Theorycraft on the bottom of the post. And, the reason you take soccerer's shoes, even on the AD or AS/on-hit build it's because the boots are a cheap source of early mpen, giving a huge damage boost early-mid game, something berserker's don't. It also affects your spells, mainly your ult. You may sell your boots after getting voidstaff, but assuring early game dominance is essential.

50 MR

40 mpen on a 50 MR target = 10 MR, 36.3% damage increase (that is, having 40 flat mpen agains a 50 MR target leaves the target with 10 MR, and would increase your damage output by 36.3% against it, comparing to the damage you would do without penetration)

40% mpen on a 50 MR target = 30 MR, 15% damage increase

40 mpen + 40% mpen on 50 MR = 6 MR, 41.5% damage increase

100 MR

40 mpen on a 100 MR target = 60 MR, 25% damage increase

40% mpen on a 100 MR target = 60 MR, 25% damage increase

40 mpen + 40% mpen on 100 MR = 36 MR, 47% damage increase

200 MR

40 mpen on a 200 MR target = 160 MR, 15.3% damage increase

40% mpen on a 200 MR target = 120 MR, 36.3% damage increase

40 mpen + 40% mpen on 200 MR = 96 MR, 53% damage increase

300 MR

40 mpen on a 300 MR target = 260 MR, 11.1% damage increase

40% mpen on a 300 MR target = 180 MR, 42.8% damage increase

40 mpen + 40% mpen on 300 MR = 156 MR, 56.25% damage increase

Getting both types of mpen will always yield more penetration than just one or another. However, we can see that, as long the flat mpen doesn't cut most of the resistance right away (like in 50mr case, in which adding % pen to the flat one gives 5.2% extra damage) or the flat mpen amount isn't too small that it's benefit is negligenciable (like in the 300mr case, where adding flat pen to the % pen gives 13.45% extra damage), the amount of damage given by combined penetration is large (in the 100mr case, stacking one mpen to the another increases damage by 22%).

The main advantage of stacking both, however, is that flat mpen is strong against low-armored targets, % mpen is strong against high-armored ones, and mixed type is strong agains all types, ESPECIALLY mid-armored ones, giving you an all-around damage boost.