Well, that was odd. 
Just finished the ice world of Mario 2. 
The boss?
A giant fire breathing fire ball. 
Yeah. A fire ball that breathes fire. For the ice world. 
Oh, you Mario makers. So quirky. Ice world was a little tricky. The ice makes you slide around. A lot. 
So far so good. Luigi sucks, btw. He can jump high, but he's a little hard to control while he's jumping, and he's slow, and can't pick things up very quickly. 
I guess I'll stick with Mario.