I got the rack version and controller so I needed an external expression pedal.
Just got delivered the Helix specific Mission EP-1 L6H. No set up needed, just plug it in with a pair of TS jacks and the treadle and button can be used independently.
On some patches I've set it as a wah, on others the speed of a univibe, on others to increase drive levels or echo mix.
If you want to go mental, then there is the Source Audio Reflex which can do all that and provide midi control to just about anything.
There are usually arguments about doing more parameter fiddling than playing - but I like sound design fiddling. But in the Helix that process is so damn fast and easy to do.
Set up 1 button to turn off a Roland Jazz Chorus clean amp with a klon drive and turn on a Dual Rec with a Tubescreamer and compressor all at the same time with zero control lag? Yup!
I've got mine plugged into the FX return of a bass amp and then either a Zilla 2x12 guitar cab or a Barefaced bass cab. I've turned off the cab modelling on the 1/4 inch outputs.... but it's still on for the balanced outputs and the USB. So FOH can have a cab modelled sound for the PA, and I can have my physical cab do the work for backline.
I haven't had this much fun with a new bit of kit for decades.