Serpentine Squiggles

A1 A2 A3 B1 B2 B3 C1 C2 C3

Entrance.

Paths to A1, A3, and B2

Optional Puzzle

Path to A1 and C1, blocked path to B2, secret path to A2 and C2

Powerup

Boss antechamber, treasure

Path to B1, puzzle blocking path to C2

End of the line.