Hippaul?

Talk to me, and you will find
I mention what I left behind.

Talk to him in Alexandria as Vivi, he mentions his secret stash of cards.
You hear a ding, a chest to find,
the treasure, of the mythic kind.

Climb the bell tower, pull the bell's rope to ring the bell (hear a ding) and you find his cards.
Talk to me, and you will hear
a challenge; now from there to here.
Later, you can talk to him again and challenge him to a race.
You cannot win, though you fret;
every success becomes harder yet.

The more you beat him in a race, the harder the races become.