Sega and Nintendo are best buddies these days, but it wasn't always that way. Once upon a time, the two companies were battling for domination of the living room via their respective range of home systems, and their mascots – Mario and Sonic – were bitter enemies that wouldn't be seen dead in the same game (how things have changed, eh?).
Given the rivalry that existed at one point, it's only natural that the developers of these two companies might find ways of secretly poking fun at one another, and one such example is hidden away in the files of the rather average (but very attractive) Sega Saturn 2D platformer Astal, released in 1995.
As you can see from the image below, someone on the development team went to the trouble of creating a rather sinister-looking Mario, and hid him away in the data files.
The description reads:
"Astal" that was released in Saturn. It is discovered that an image that seems to be Mario was hidden in 0xFE90 of APT.BIN on the disk.