Game link: www.roblox.com/games/58240131...
This is actually my 2nd time completing everything before error swap, so this is why I do not get the badges for those modes and bosses
The hardest boss in this entire game is Error swap and I'm not even kidding. This is like some video proof difficulty boss, not gonna lie. The amount of rng you have to have to beat it is insane (1st and 2nd attacks are mostly rng, so if you do not get lucky with the big red bone on the 1st attack or with the black bones on the 2nd one, you're done). You get only 15 lives to beat him and if you do not beat it (which obviously is going to happen, because this fight is so dumb), you have to rejoin the game AND WAIT FOR 5 MINUTES STRAIGHT JUST TO TRY THIS AGAIN. I'm not even mentioning the idiotic 1st platform attack, which not only has this big red bone that almost one shots you (or leaves with half hp), but also the stupid platforms themselves that somehow magically can kill you, because your leg clipped through them and you touched the death floor. 2nd attack is very annoying because of the bone zones that leave you barely any time to pass. Tried going through them half a second later than needed? You're dead, no questions asked. Side blasters aren't a big problem, however, sometimes they can do a lot of damage and most of the times it's fatal for you, because you get damaged by the black bones next. 3rd attack is easy, but if you get to it with low hp, you're probably not passing it, because it's very easy to get hit by the black bones.
Maybe, I wouldn't have complained about all of this, had the god damn fog let you see ANYTHING. Or at least there wasn't a death limit, so I didn't have to wait 5 minutes again in the lobby. Gladly, I've completed it and it's over, took me like 2-3 hours on this boss, despite it having only 3 attacks (most of this time is probably from waiting for the orb to spawn).
Here's a list of the hardest bosses from each mode (for no reason):
Normal mode (swapswap - dio papyrus): reaperswap
Hard mode: horrorswap and hyper dustswap (a little bit)
Extreme mode: horrorswap and reaperswap
And, of course, errorswap (fatal error is very easy)