In a preview event for Metroid: Samus Returns, Nintendo clarified to USGamer the specifics behind the amiibo locked Fusion mode within the game. As it turns out, a regular hard mode will be unlockable without the need of any amiibo, but a separate “Fusion” mode, which also grants the player access to the Fusion Suit from Metroid Fusion, is only accessible via the Metroid amiibo.
Yes, Fusion Mode—which will give players access to Samus’ Fusion Suit as well as a more challenging difficulty in the game—is indeed locked behind the Metroid amiibo. This content will not be offered as a separate DLC in Nintendo’s digital eShop. However, there will be a standard hard mode that will be unlockable once players complete the game on regular difficulty.