Firstly, it'll be out in Europe on December 11th (next Friday) while North America gets it on January 6th 2016. It'll be sold at £10.99 / $12.99, 14,99€.
The reason for the delay in North America is due to only a limited stock being available to ship before Christmas. By waiting until January, Yacht Club is ensuring that there will be plenty of amiibo units to go around.
As to the amiibo itself, it is compatible with 3DS and Wii U versions of Shovel Knight and unlocks new content inside the game.
If you scan the amiibo on the world map or save file select screen you'll unlock the following:
- Level up to a max level of 50 by finding treasure
- Earn relics in an all new way while uncovering all-new relics, abilities, and powers you never thought possible
- Customize the look of your Shovel Knight with cool and crazy cosmetic options
- Use your Custom Knight seamlessly between Nintendo 3DS and Wii U
If you scan the amiibo on the Challenge Mode screen then you'll get:
- Battle your way through amiibo exclusive challenge stages that take advantage of the new Custom Knight relics and abilities
- 5 new solo challenges and 5 new co-op challenges (exclusive to Wii U) await
You'll notice there that the co-op challenges are exclusive to Wii U. In fact, the Wii U version gets co-op throughout the whole game. It's the only feature the 3DS version doesn't have.
There will also be more that the Shovel Knight amiibo can do with the game it's from. Yacht Club will have an instruction manual with all of those details at a later date.