This is a green potion made of pixels. The resolution isn't high enough for it to bubble, but if it was, you can believe that it'd be bubbling with HP and MP restoring goodness.
This item shaped like the red and blue life potions in the 1987 NES game, The Legend of Zelda. The HP/MP restoration scheme is closer to the next installment in the series, A Link to the Past. However, KoL's mana and cure-all colors are switched, as Jick staunchly holds that mana/magic should be represented with blue.