AP Varus is so much fun to play. Holy shit. Get nashors/malady first into Deathcap/Abyssal and the burst you do is crazy.
3 AA's > Ult will take someone to about 50% hp just like that due to the burst. Perfect combos include 3 AA's > Q/E/R > 3 AA's > Q/E/R > 3 AA's > Q/E/R. His damage and combos look really easy on paper but he is incredible hard to pull off in game.
He has no escapes, and being a burst mage its quite hard to do anything. He has low range due to his 550 range. And he is really item dependant due to AD carries having weak early game stats and base stats due to the power growth they get through items.
AP Varus is fun, no where near viable.
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New Black Cleaver going to be standard on nearly every bruiser.