There are 15 medals to unlock in the game. Each one will also unlock a customization item, something that you can use on the character customization menu.
Get 3000 points or more in the fishing mini-game - Awards 'Red Skin'.
Complete the game - Awards 'Eyepatches'.
Dig up 3 hidden items - Awards 'Black Pearl' and 'Thunder Earring'.
Meet Douglas Gavelin in every city - Awards 'Ghost Mask'.
Fight 20 Flawless battles - Awards 'Devil Mask'.
Fight 50 battles - Awards 'Top Hat' and 'Demon Eyes'.
Get 1 Lucky hit in battle - Awards 'War Paint Tattoo'.
Get 10 Lucky hits in battle - Awards 'Gray Skin'.
Complete the Summoner's challenge - Awards 'Eyebleed Tattoo' and 'Eyeshadow Tattoo'.
Fight 10 battles - Awards 'Bandana' and 'Bloodshot Eyes'.
Santa's Little Helper
Complete 10 sidequests - Awards 'Anonymous Mask'.
Collect 50 mushrooms and/or butterflies - Awards 'Serpent Nose'.
Soul of a Poet
Find all 3 poems - Awards 'Masquerade Mask'.
Obtain all swords - Awards 'Masked Cape'.
Fight 25 battles - Awards 'Fedora Hat' and 'Undead Eyes'.