Johan use a P-bass + Ampeg SVT. The rest I'm sure of, but Mew is brilliant!
I think he use standard tuned bass, but like on Am I Wry? he use octaver + some fuzz.
If you see the live in Copenhagen DVD you will see that he plays the same bass on most of the show (no time in between to detune a bass!). So it is down to the effects.
I don't think Johan or Bastian (the current bass player) use lots of effects. Sound mostly like amp overdrive with some additional distortion (and octave on some songs like Am I Wry?). But still, the bass tone is not that easy to replicate! Johan tend to play quite different live than studio while Bastian plays more like the original cover.