Talk:Xerath/@comment-84.188.122.243-20120105105425/@comment-60.241.118.81-20120106073919

i find it wierd that no-one seems to understand how the magic pen works, its worthwhile getting, but definately not early, MR stacks multiplacitively so, this is how i remember calculating it

pretend they have 100 magic resist 30% pen due to Locus of Power from the remaining 70 magic resist 40% pen due to Void, this applies to the "REMAINING" magic resistance so 40% of 70 is 28, leaving him with 42 magic resistance and finally 10% due to the mastery, 10% of 42 is 4.2, pretty much 4 so 38 is left 100-38 = 62 62% magic penetration its worthwhile getting, but much later on in the game because no matter how much they stack magic resistance, destroying 62% of it cripples its effectivenesss by a lot