Zero (Ar tonelico: Melody of Elemia)

The last among the liquid metal robots, and the third strongest Robot-type enemies, the Zero retains the physical immunity characteristic of this sub-type of monster, and its moveset is pretty much an expanded form of the Type Zero's, the only differences being it also has the S-KILLER from the Type Un-Zero, and that it can prolong the battle by restoring its own health with Self Recovery. Due to this, make sure to annihilate it quickly, although due to its elemental resistances, you'll have to either employ a non-elemental attack, or wind magic like Aurica's Sylvan Dance.