Dr Mario Modding Oddity - Modding l'écran titre buggera le jeu

Présentation d'une étrangeté du Modding de l'écran titre dans Dr Mario.

[@Apalapan97]

I don't understand French very much, but maybe what is in Dr. Mario's article in TCRF could be of help:
"The game features a simple anti-piracy check that will intentionally crash the game if the title screen is altered. On reset, the game performs an 8-bit checksum of the area of ROM containing the title screen tilemap data ($B900-$BDFF). If the check passes, RAM address $740 is set to 00 and the game runs normally. However, if it fails, $740 is set to FF instead. This address is checked whenever a pill lands; if it's set to FF, the game pulls whatever value is stored at RAM address $53, pushes it to the stack three times, and performs an RTS. This causes the CPU to jump somewhere in RAM, and since there's no valid program code there, the game soon crashes.
Interestingly, a very similar 8-bit checksum routine (and method of crashing) appears in Final Fantasy. Perhaps the programmers drew inspiration from NASIR?"

[@zigaudrey]

So, the checksum part is correct.
If we remove that checksum or turning that FF into 00, we could freely modding the title screen.
Interestingly, editing the game background don't cause issue.