Scenario: After his final battle against Freddy, it is revealed that Balloon Boy actually survived the cataclysm. However, as a consequence of the temporal paradoxes, one of his timelines merges with that of another game: Undertale, specifically during the Pacifist Route. Because of these distortions, Frisk is replaced by Balloon Boy and realizing that something is terribly wrong, Asriel begins to question what is happening. The temporal anomalies initially leave him confused, but he quickly comes to understand that Balloon Boy is the one responsible for these distortions of reality. With that realization, the battle between the two finally begins.
So save/load is effectively a non-factor here due to Balloon Boy's time compression shenanigans.
On top of this Leviathan is passively absorbing energy within this new timeline which he noted if he reached this state in the game time would break on his whim putting Asriel at a disadvantage.
Asriel's attacks could work but he could also easily get mind controlled by BB.
Now on the other hand, like I said, Asriel's attacks can work as they directly target the SOUL and as far as I can tell in FNaFB, the reason Balloon Boy even remained as a Phantom was there was no way to affect his soul, which means attacks from Asriel would be a serious threat.
Though Balloon Boy has a passive skill that increases his dodge rate at the same time.
There's also the important thing of monsters innate weakness, Balloon Boy is full of hate and vigor which would likely massively weaken Asriel.
Due to a lot of the unknowns I'll say this is likely an inconclusive as it's dependent on if Asriel can hit him or if Asriel is weakened enough to where End of Everything could kill him in one shot.
Couldn't Balloon Boy take advantage of the disadvantage that due to hatred, monsters are weakened to control Asriel's mind? I think it is possible and since the increase in speed would allow him to dodge the attacks I see him with a little advantage due to that very reason.
It could be possible, I don't know if it's ever outright noted that monsters resistances weakens but it would fall into logic since all of their stats drop. I can agree with BB taking it 60-40 through that.
FnafB is a normal RPG which is something Undertale is going to cry against. Moves like Sea Shanty, Facial Recognition, Curing Ring...all these moves mixed with his overwhelming hate that's going to weaken Asriel more...it'll probably be too much and just BB to overwhelm Asriel
