When Mario catches fire in Super Mario 64, black smoke pours from his rear end, along with a heavy smattering of black garbage pixels. This is due to a mistake in the game code that displays the texture in the wrong format. The black pixels should actually be transparent. The bug went largely unnoticed for 24 years.
A new patch by Zoinknoise restores transparency to the effect as it was intended. The patch adds no new art or outside assets, it simply displays the smoke in its correct format.
The effect as the game’s designers intended it to be seen
Source: https://twitter.com/romhackingnet/status/1240316167249526784
Patch: https://www.romhacking.net/hacks/5008/