I know someone has probably already asked and may ask again but with all of the recent changes and me being a fairly new player I was wondering what the best Rune stack and mastery stack would be with Master Yi when I mostly build some Attack Speed and Life steal with a lot of damage?? mainly using Phantom Dancer, Blood Thirster, and such.

Flat Armour Seals and MR Glyphs work for all melee's
It might not be the best but it's standard.

for master yi is either desolation/alacrity/strength marks/quints.
Desolation probably the best I'd think. A mix of alacrity/desolation if you jungle.

I have multiple rune pages that I play around with, when i play master yi, i use one of these
Marks: ArmPen
Seals: Flat Armor
Glyphs: Flat CDR
Quints: 2 Flat HP, 1 ArmPen

Marks: Attack Speed
Seals: Flat Armor
Glyphs: Flat CDR
Quints: ArmPen

I really only have the CDR because i already had them, and don't have too many different glyphs.
Master Yi gets 70 AD from wuju style, which is a BF sword and a pickaxe. Because of this, i feel attack speed is better in early game.