Quote:

**Hyco**:

But why not go all Magic pen glyphs with Magic pen quints?

Ok some basic theorycrafting. Lets assume a .8 ratio, on a single target spell. Flat AP quints x3 will immediately add approximately 12 damage for each cast, whereas MRPen quints will effectively ignore a certain amount of the MR. Hence, you'd expect an increase in both base, and AP bonus damage. The nature of MRPen is that it is only superior when the amount of damage increase provided by it is superior than the amount of AP multiplied by its respective ratio. Thus, in this case, you'd need an increase of 12 damage for it to be worthwhile, before MR. How much is that? Keep in mind MRPen makes it effectively calculate your targets MR to be lower by that amount.

let damage = d, base spell damage = b, magic resistance = MR = 30 (base), and MRPen

damage reduction via MR = MR/(MR+100)

Thus dmg received equals (1-[MR/(MR+100)]) multiplied by the amount of damage of the spell cast. Assuming the MRPen equals 3*1.96 (ie. the amount received from 3 quints)

Firstly, flat AP quints provide 12 bonus damage, assuming a .8 ratio, thus, you'd deal 12*(1-[30/(30+100)]) = 9.2 damage additional.

The

**additional** damage due to MRpen equals the damage taken after applying it minus the damage taken before applying it

9.2 = b(1-(30-1.96*3)/(130-1.96*3))-(1-(30/130))

b = 9.2/((1-(30-1.96*3)/(130-1.96*3))-(1-(30/130)))

Thus, with a .8 ratio on the spell, you'd require the base damage to be greater than or equal to 252 before MRPen quints will provide additional damage. This isn't including any bonus to damage through AP glyphs or, well, any source.

To put this all into perspective, you need to consider the amount of AP bonus you will have, and when you will need the most damage. The bottom line is, flat AP provides you with a hefty amount of bonus damage at the lower levels, and MRPen doesnt start scaling better until after the first 15 minutes or so. This bonus damage helps an exceeding amount early game, which is when most games are decided, hence most players decide to go with flat AP quints over MRPen quints. If you will quickly get more AP, MRPen starts to shine very fast.

Note: I havent double checked all that math and I just pulled an all-nighter, so it may be off. If someone wants to confirm or refute either way it would be appreciated.