Void staff vs Liandry torment on ap kog

Why not both? Though, if choosing one, Voidstaff is probably the better option as, he can only make the most of Liandris if the enemy is in his slow field, and he already has tank shred with his on hit. He really doesn't need the extra health from Liandris either.

void > liandris

kog doesnt really make to good of the %health thing since hes not a dot mage hes a poke siege mage artillery monster. and besides he has %health on his w anyway

void staff is better because %pen is more effective, flat pen is better for people who really only have 1 magic item or less, then its good. otherwise a sejuani with locket/banshees/spirit visage etc etc flat pen is almost negligible.

void will make sure you deal more damage and can kill things, liandries if you just want to poke and you aren't your teams main source of damage and you just want to apply the burn.