Did that. downloaded the image, named it !$omegadeath and it didn't work. changed it to !%24omegadeath and then it did.
However, after going through the intro I get another error saying " Fail to load: img/character/%24DarkForestLight.png.
So I went to the file and found a $DarkForestLight. I changed the "$" to a "%24" and it worked again. I haven’t gone that far into the game but so far I didn’t get another error of the same nature.
By the way, this is within the 21.1.b version, also in html. Running it through itch’s launcher in linux.
Edit: Got it again at the Gym in village at the start of the game. %24BigMoster1.png.
I think its safe to say that this will be happening throughout the game.