Shadow Beasts

Shadow Beast has transparent and featureless humanoid form. Its eyes glow yellow like Dire Ghost's do. Its only form of combat is hitting with powerful claws.

Despite what the lore says, this creature is not totally invisible. It only goes invisible briefly during the combat and reappears at slightly different position, making hitting it difficult. Avatar encountered only two of them during the Ultima Underworld I. Shadow Beasts haven't been seen since, probably destroyed by the eruption of the Abyss.