After Clearing Story Mode and watching the Credits, you will unlock new Game Modes on the Menu. The Arena is a Mode where Kirby fights against the Mini Bosses from Story Mode in a row. Dedede Tour is a Time Attack where you play as King Dedede in the Stages from Story Mode, with harder versions (called DX/Deluxe) of Mini Bosses.

Mode	How to unlock
Dedede Tour!	Clear Royal Road Stage 6 and Defeat the Final Boss.
The Arena	Clear Royal Road Stage 6 and Defeat the Final Boss.