Some enemies occasionally glitch. An example is a stalfos enemy. Some spawn correctly while others use junk tiles. Literally two of the same enemy are on-screen (well, more in this case, but two just refers to more-than-one), and one will decide to use random tiles for its animation. The stalfos in question was never altered, uses tile 3960, 4-frame 4-direction (so 16 tiles total), and is just a walking enemy. ALL instances of tile/graphics glitching makes enemies use tiles in the 6-19 range O.o
EDIT: No, the glitch uses the first row of tiles on the tilepages. the very first row.
EDIT2: And apparently a handful in the second row.