There's a reason I brought up the Smash Ball, and it's because of another theory that I had regarding the night damage.
In the game, characters can attack the Smash Ball to gain access to their "Final Smash". The final smashes vary from character to character, but most of them tend to be a large attack that deals huge damage and has massive knockback potential. Most result in OHKO's, or KO at low percentage. If they don't OHKO, then they deal a lot of damage. And most of the time, it's impossible to fight back if someone has used their final smash on you. Typically, they're KO'd before they have a chance to retaliate. Seems familiar, no? Also, some characters are able to absorb other characters into their final smash as it's going, but the later a character gets stuck in it, the less damage they receive. So is it maybe possible that someone used their final smash on Eduarda and other players, such as myself, got part of the damage from it? It would make sense this way if Eduarda was unable to attack back. It would also explain how multiple people have been receiving damage at night. Obviously other items are probably at play too (as Doc claims to have thrown a boomerang, which hit two people), but there is still some damage unaccounted for. The Smash Ball is a really important item in the game, so I wouldn't be surprised if it was in this one.