he is pretty strong, but not invincible. He has no built in mobility besides his leap strike.. so you kite him as he tries to chase you down, never proccing stun as you kill his teammates. If he goes ap, and does big damage on hit, you treat him as a caster, build items to counter and do the same. Against Jax mobility is key, just keep away, and push towers, and targets. The worst thing you can do is try to focus fire him down or auto-attack without a sword of the divine. Be cautious of where your creep waves are and who they are attacking, and treat Jax like Ryze with distance, and late game you should be able to out push. If you catch him by surprise, which is often easy to do, burst him down. It may be slightly worthwhile to turn his passive down slightly.. I dunno.