The Japanese-only 3DS title One Piece: Super Grand Battle! X is receiving Amiibo support through an update this winter. Much like Mario Kart 8, the Amiibo will unlock special costumes for the different characters. For example, Luffy gains both a Mario and a Luigi outfit, Zoro gets a Link costume, and Sanji receives a Fox ensemble, among others. It’s great to see 3DS developers starting to take advantage of Amiibo on the handheld!
Source: Arlong Park Forums