I was looking for SK music when I stumbled across this video:
https://www.youtube.com/watch?v=3iXdrHGSDhw
The picture specifically intrigued me because it shows all the bosses together fighting one knight. That got me questioning, why can't we have a fight 'em all/ true arena (Kirby reference)/ boss battles mode(SSBB) where you can face all the bosses just for a challenge?

In this mode you can fight all the bosses in one giant room together with no obstacles like falling shadow fire/walls/regen slime turrets/scuttlebots/slags to make it slightly more balanced. (this would still not be OP because think of how easy it is to defeat them with professionals) other accommodations would include no RT lasers (also they hurt enemies as well fyi), no Vanaduke remains to obstruct the player(s), possibly a new way to defeat Snarby, no Vana rushing?, etc. It would be more improbable but it sure would be fun!

Another, more viable way to do it is to have separate rooms that have all the obstacles as normal, but there are literally no arsenal stations to change gear! Good Luck facing all of the bosses with one loadout! But it wouldn't be hard to string together the boss rooms.

SL alternatives would also have the swarm, SL versions of bosses, possibly with some/more obstacles to increase difficulty.

There is no real incentive to do this as no seals are distributed upon the defeat of each boss (which could lead to some issues), though crowns that are usually dropped may appear and there might include a treasure room like in the danger rooms. If OOO wanted, then they could even work this into the plotline, as the swam grows.
Then again someone might have already talked about this. /shrug. Your thoughts and comments?