Pedals that stack with the TC Electronic Classic Sustain

Catalinbread Giygas

Catalinbread Giygas's own octave character is the real reason this is worth trying

Electro-Harmonix Big Muff Pi

Electro-Harmonix Big Muff Pi leans toward fuzzy, and that's a real, usable character to pair with

Electro-Harmonix Canyon

Put Electro-Harmonix Canyon after TC Electronic Classic Sustain in the signal chain, clear of TC Electronic Classic Sustain's own gain stage — goes in the amp's FX loop (or last, into a clean amp)

Empress Echosystem

Keep TC Electronic Classic Sustain's sustaining voice out front: Empress Echosystem goes after TC Electronic Classic Sustain in the signal chain so its pristine voice doesn't muddy it — goes in the amp's FX loop (or last, into a clean amp)