Fighting Ring challenges:
Beat the first stage.Bonus Arena Challenges:
Beat the game to unlock Arena Challenges 41 through 50. Beat those to unlock Arena Challenge 51.Hard mode:
Beat the game under normal difficulty.Chihuahua Race:
Beat Stage 3, then talk to the guy in the shop.Alternate costumes:
Beat the game to unlock the Carnival, Devil Hand, Karate, and Olivia's Bunny Girl costumes. They can be obtained by starting from Stage 2 then talking to the new NPC in the shop.
Thanks to Revolution Readers Shoni and TheTeh!

Embark on an inspiring mission of human connection beyond the UCA. Sam — with companions by his side — sets out on a new journey to save humanity from extinction. Join them as they traverse a world beset by otherworldly enemies, obstacles and a haunting question: should we have connected?