The Korg NTS-1 is a versatile multi-FX unit in a tiny package, and it's a full-fledged monosynth that uses the Logue SDK (from the Minilogue and other synthesizers), so you can load custom oscillators and FX of any kind that other people have made themselves and put online. You can find a ton for free, or you can purchase the very excellent Sinevibes oscillators and FX.
Even if you ignore the monosynth and arpeggiator, this is an astoundingly good sounding multi-FX unit. Tons of different types of Reverbs and Delays, but also there are flangers, phasers, auto-wahs, tape stop FX, ensemble, bitcrush, and whatever else you can find out there on the net.
3.5mm audio jacks have been RE-SOLDERED and hot-glued on the inside for stability as well.