I really wish you could add hit points to enemies and make certain enemies required to be defeated before a door or pipe appears.
Bosses feel kind of lame. The only solution is usually to set up some convoluted system where you use Clown Cars that are required to progress, or Kamek/SMB3 Bowser who need to destroy blocks to progress.
The majority of boss fights people seem to set up are easy to just jump over or tank a hit and run past. When it's clear they didn't intend or want you to do it that way.
Yeah I was looking for this functionality too. I've seen some people get creative like having stacked donut tiles that take a while to fall, so you'll probably get hit if you haven't killed the boss yet, or the Clown car like you mentioned.
It's interesting because small boss fights and challenges seem like a not uncommon occurrence, at least in recent Mario games and SMB3.