M-Slowbro is lucky it has Slack Off, given how useful Regenerator is and having to give it up for Shell Armor.
>>20476023I like to think of it as mutualism rather than parasitism.
The Shell has always represented increased defense for Slowbro (vs. Slowking's head clamp for SpDef and Slowpoke's middling stats). The way I view it, its evolutionary path is to maximize defense. Instead of just taking up the tail, it now takes up the entire body (freeing the tail). This is indicated by its new ability, Shell Armor.
If anything, Slowbro's body pushes out and leaves little room for the Shellder, likely having broken through many of the inner shell compartments.
