Which runes should you get for blue glyphs with the recent buff announcement to flat ap?
My top 3 played mages are kennen, vlad, cass
and I sometimes play brand, karthus, and kass
I usually run magic resist/lvl but got some money to spend
thanks for your help

bump for some help

Magic Penetration.

It offers a % damage increase for all of your magic abilities, and a lot less champions gain magic resistance naturally, and unless they're directly countering you, they won't build it until after the mid-game, meaning a larger portion of time to dominate. AP runes, on the other hand, offer, at best, 1% damage increase at level 1 (per rune). The bonus they give is less effective the moment you buy AP items. As well, unlike AP, where each point of AP is not as strong (relatively) as the point before it (same with AD), Magic Penetration becomes stronger the more of it you have (up until the enemy is at an effective 0 Magic Resistance.) This means, with a pretty common mastery setup, and buying Doran's Ring at the start, you are already overshadowing the effectiveness of your AP runes. Yes, on certain champions like Vladimir (who has a heal based on his AP, not on his damage), more AP is better, but the differences for those particular champions are close enough that it's an either-or pick. For everyone else, Magic Penetration runes are better.

but doesn't magic pen get useless pretty much once you get void staff?
and pretty much no one can afford to start with dorans ring anyways unless you are playing against noobs that don't harass at all
you already have some magic pen from red

I guess useless was a bit strong
shouldve said less effective

Kennen:MR Blues Flats
Cass:AP Flats

Take 4 Flat AP glyphs and 5 AP/Level Glyphs with some magic penetration.

Is magic pen on glyphs any good? that's the question, for reds sure, for blues...

Casters are very diverse and I dont play them often, so I cant offer anything myself, super circumstantial question, and I almost always favor defense, but AP glyphs are kinda cool on Vlad :]