Type Zero (Ar tonelico II: Melody of Metafalica)

While these monsters are a massive improvement over all the previously encountered Robot-type enemies when it comes to stats, particularly due to being able to halve the damage from Wind and Thunder-elemental attacks, unfortunately that only makes them harder to kill, as they only have one attack. That is Z-STAB, which can inflict the Pain status, but since it is so easy to block, it would be hard for it to become a threat to any player.