Like most late-game carries, you'll need to punish them early and often.

Your roaming support will hopefully help punish them, especially if they are greedy. Short of ganking often, hindering their farm and gold gain will be good to prevent them taking over the late game. Those steps can be good outside of mana-burn strategies.

Also, keep in mind mana-draining items like diffusal can come in handy, especially in the hands of illusion heroes like PL. Each hit can rob Medusa of her shielding.