(hex:7D) is a glitch item in Pokémon Yellow.
Using this glitch item both in and outside of battle will cause a long HP bar to appear on the screen that continues to reduce until a certain point. Outside of battle this HP bar will be represented with letters like "C" and "L", while inside of battle the HP bar appears properly.
After the HP bar finishes draining, the game will print the text "(POKéMON) recovered by (X)!" and the quantity of the item will be reduced by 1. If used outside of battle a HP bar with glitchy menu sprites will appear and closing the menu will cause the Rival's effect.