So, after fighting zombie dragon and changing to Piranha-Man I went to the volcano where I found a changing platform (where you change to Mouse-Man and get the Thunder Ring). There I changed to mouse-man, and kept it since I wanted to know what secret treasures might be in the town's tower.

Now, I can't find a way to change back to Piranha-Man.
I can't get back to the volcano platform, as that would require Piranha man to get above an underwater obstacle.
Seems the zombie Dragon is gome for good, so I can't let them curse me into Piranha-Man again.

I guess the next path would be to get into the underwater shipwreck, but I can't get there until I can swim around obstacles.

Can anybody recommend a place to go next?
I've tried opening the passage below the tower with the Thunder Ring bat that's awfully hard o_0'

Wooho :D Thank you. I've never looked in this direction.
Thank you!

[edit: since I've run past it at least three time, here's a screenshot for others that might hit the same problem]