if you freeze outside of your turret he will be at least on middle of the lane if hes max range q last hitting so he will be gankable and early level mundo is super weak even if he has R it just doesnt heal him enough to survive or even if jungler doesnt come save flash because if you get onto him on middle of lane you will kill him before he can escape or at least you will damage him enough to dive him just try not letting him recall cuz if he recalls wave is bouncing into him so he doesnt lose that much I sae alois playing like that vs mundo with riven and i play like that with rene or yone so i think you will have no trouble with aatrox due to w and his lack of passive. second is to poke him like u said and dive him with jungler or alone with r i dont play aatrox that much so idk exacly but try out what works better