Knack is a third-person brawler featuring a protagonist assembled from ancient relics. The story describes how a species called Goblins, led by Gundahar, attack mankind. Knack joins industrialist Viktor to fend off the Goblins, working together with security robots. The game presents a series of arenas linked together where Knack must fight off opponents to progress.
Knack attacks with his arms, performing combos and can also jump and dodge. Throughout the game, different relics allow Knack to take on alternate forms. As Ice Knack, he has more protection but receives damage through melting. Metal Knack is very strong both defensively and offensively, but magnetism opens up a weakness.
Regular relics allow him to grow in size or reverse the process when damaged. By defeating enemies and smashing yellow crystals, sunstones are collected that fill up symbols. Once full, Knack can unleash powerful moves such as shockwave, storm, and blast. He can also transform into a larger form, often triggered automatically for specific sections.
The game has thirteen chapters with secret rooms providing additional relics or parts used to create gadgets. These allow Knack to slow down time or enable a damage multiplier. The game uses a fixed camera that changes when accessing new locations.