YAY0 Compression

Paper Mario uses an LZ77-type compression format called Yay0 to compress much of its assets. Yay0 is nearly identical to MIO0, except the maximum match length has been extended from 18 to 273. It manages this by storing additional length information in the data section. Yay0 encoding was also used in many other N64 games, as well as some early Gamecube games.

Compressed texture replacement tutorial

References