In the 2nd Floor, you can also find Crasher Wake from Sinnoh there.
Talk to him and he'll give you three accessories: the Chimchar Mask,
Piplup Mask, and Turtwig Mask. Cool! Other than that, you can see
Maylene — another Sinnoh Gym Leader — doing some "training" in the
Restaurant in the southeastern part of town.
Source- http://pokemon.marriland.com/hgss/walkthrough/rainbowbadge/celadon_city
Hope this helps =P
