Dosus aren't necessarily as big as a building, despite being like so originally Dosu are big yukkuri who can shoot sparks and have an aura of easiness around them
That aside the artist left a comment to the picture saying it was a dosu being used as a punching bag
welp, spark or no spark, as long as their mushrooms are taken away, they'd be rendered unusable anyway :p
Some stories do not really require them to have their magic mushrooms. In some stories they can use their life force to power up a spark that will likely kill them afterwards.