Which AP Assassin scales best into late game?
List:

List:

is the best scaling AP assassin in the game.
Second place goes to
and
imo.
and
are probably the worst AP assassins in the late game.
Kassadin 100% is the best AP assassin lategame, and Sylas is the best teamfighter out of all of those. Pretty much all the other ones fall off after mid game. Katarina namely, her teamfight is terrible and one cc and you die, she only shines when the enemy team has zero cc but you were likely to win that game anyway. The rest will always be able to one shot a target lategame at the very least.
Ahri, Sylas and Diana are not assassin's anyway.
Ahri's a Mage, Diana's a Diver, Sylas is an AP bruiser.
Kassadin and veigar 100%
ap into late game?
umm... fizz.
…
My main, she has everything you could want. Low cd plus ult unlocked at level 1. Passive that gives you increased dash (or pounce) on Cougar forms W if you land a a spear. The spear has a lon g range and the further you throw and hit menasm ore damage. She has AoE, massive heal, a hunt passive triggering trap, a bite (could be used as an execute), and even an insignificant passive that gives you extra MS in bushes. And to make sure you don't wall from lategame, take Dark Harvest on her, your dmg will be very strong throughout the game even if you are behind.