Pokkén Tournament will be compatible with all amiibo, not just Pokémon-related ones, according to Nintendo’s amiibo page.
First-run copies of the Pokémon themed brawler for the Wii U will ship with a special Shadow Mewtwo amiibo card, which will unlock the character in game. Previously released amiibo will function differently however, instead unlocking in-game items, the Nintendo website states. The nature of these specific items is unknown as of yet.
Item usage was not an option available in the original Japan-exclusive arcade game; which, along with the new amiibo functionality, marks a notable difference between the Wii U version and its arcade counterpart.
Pokkén Tournament’s official website has a tab- which is currently inaccessible- that seems to detail how the amiibo functionality will work.
Pokkén Tournament launches worldwide, exclusively for the Wii U, March 18.