Hey guys,my mains are 
ive also started playing 
recently ,so all of these are ap so for my runes i use magic pen reds,ap blues and ap quints,im deciding on my yellows i had health but i think i wanna go for cdr ,some peoplesay it isnt worth it ? am i better off with something like mr yellows? pls help (:
Hex the FenFen1 votesI usually go for scaling health yellows for a lot of my mid laners. I main Zyra mid and i do really well with it. Also are you running scaling AP blues or flat AP blues? the scaling ones are better i find
AlldaySkandi1 votesi have flat ap blues ,are the scaling ones much better?
Hex the FenFen1 votesIf you play some mid laners with good late game pressure. Ahri is one for example. I often play mages that excel in the late game and those blues really help
Fauxfire1 votesI main 
, so this is my advice.
For , since I need less kill pressure with my poke and wave-clear, I normally take magic pen marks, scaling health, flat AP quints, and scaling AP glyphs. Ahri has a very scary late game presence and your quickness plus naturally low cooldowns makes CDR less an important stat, so one CDR item (
or 
) is good with scaling AP.
As for , he has awesome lane kill pressure and scaling AP glyphs doesn't help with his roam or early game potential, so flat AP glyphs in exchange for scaling AP if not magic resist for survivability is a better choice. It's a good example for other AP assassins (pretty few naturally).
Not sure if CDR runes are so great, but in a comfortable match-up/composition I take scaling CDR runes on 
, but almost always take scaling glyphs on hyper late-game champs like , whether it be AP or CDR. Usually CDR, since re positioning soldiers and self-peel from your high CD ult is so vital.
Except SOMETIMES in Diana's (attack speed?) case, nearly always take magic pen marks and flat AP quints. Scaling AP quints don't scale fast enough and you NEED wave-clear and some sort of pressure in lane. Even if you are . Marks can vary, but break down to about only two different runes: scaling health and armor. You're and you can't wait to get into lane but you have to face a 
. Great. This guy does so much physical damage and plays so safe AND pokes well that you need armor seals to survive and out-trade.
TL;DR/Breaking it down:
Marks - Use magic penetration. In few cases where you want attack speed for clear or better kill pressure, nothing really compares for magic damage champions like the magic pen.
Seals- Highly depends on your match-up or their map pressure. Scaling health is great for mages with range who naturally will take less harass or few to no minion damage, but if you are facing an attack damage caster or take lots of harass because you aren't ranged then go armor seals.
Quints- Flat AP. End of story.
Glyphs- If you scale well late game and have good lane pressure from your good clear or poke, scaling AP is for you. If you have amazing kill pressure because you are an assassin, go flat AP. If you are against cc/burst and/or you are in a weak match-up, magic resistance.
AlldaySkandi1 votesthx (: