I was reading this and thinking about how the Line6 HX Effects or Stomp can get so weird once you let it. Sure it is straightforward and vanilla as advertised, but the expression pedal mapping to multiple parameters and the most recent Glitch and Poly effects make it worth considering. It plays so well with other pedals making room for weirder devices so you don't need an individual device for an effect you don't use that often, not to mention all of its utility functions like EQ, compression, and tuner.
My favorite weird expression pedal combo:
Heel: Pitch unison; Vibrato depth and mix set to min, any reverb or delay mix off.
Toe: Pitch up +2 octaves; Vibrato depth and mix control set to max, 16th note; Any reverb or delay mix to taste ( usually ~30% for me).
What that gives you is your basic tone in heel position, but when you ramp up to toe position it gets high wide and wiggly! I figured it out trying to cop the synth sounds from a dubstep Flux Pavilion track with a L6 M9 years ago. I still come back to this because it is just so fun. Add effects to the heel and fade them in and out to make it even cooler. Endless options.