Just to jumpscare Present TSC in that giant fractal dodecahedron? I don't know. Where would he go after Present TSC falls into the shape?
Also, I headcanon that Physics actually takes place after Geometry, because Present TSC starts the episode by falling...which could have been started by falling from that dodecahedron. Maybe TSC is locked in some sort of trial chamber by traveling through all the universes (Math, Geometry, Physics, Addiction) and has to do enough to get out or something.