Laning as kassadin isnt anything simple. You have to respect every oponent that is playing against you because of kassadin's horrible early game. You want to play as safe as possible at early levels. Try not to miss a lot of cs because they are the reason why u will be strong in the late game. What u want to do is to push your lane and try to roam bot lane if u see that enemy bot lane is pushed out. It will help you snowball especially when u have dark seal. In the late game you want to buy mejai's only if you are ahead or you have fully stacked dark seal. In late game kassadin transforms from mage to assasin so you want to make picks when enemy is solo.