All chapters:
To unlock all chapters, load a profile and go to the chapter selection screen. Press Right, Right, Up, Down on the D-pad, then 2, 1, 1, 2. You will not receive any health upgrades when jumping to a later chapter.
Concept art:
To unlock all of the following concept art at the gallery, collect 450 grubs.
High-Res Creature Renders and Concept Art
Environment Concept Art 1
Environment Concept Art 2
Environment Concept Art 3
Environment Concept Art 4
Box Art Concepts