Type Un-Zero (Ar tonelico: Melody of Elemia)

A greatly improved version of the Type Zero, this monster still retains its annoying immunity to physical attacks and the Z-STAB, but it also gained the stat-boosting S-BOOST, and more importantly, the dangerous S-KILLER skill, which has a chance of instantly killing its target. Due to the above, you'll have to destroy it as soon as possible, and be always prepared to revive fallen party members.