Poison Drake (Ar tonelico II: Melody of Metafalica)

Technically speaking, these monsters aren't a large improvement over the Blue Wyverns when it comes to stats, yet their skillset, despite being less in number, is still more dangerous. These monsters can use Swoop, which hits a party member once; and Poison Mist, which hits all party members four times and inflicts the Virus status; thus reducing the amount of health regained through the usage of healing items and Song Magic. This last skill is what makes them a threat, so it's extremely important to block it correctly in order to minimize damage and avoid getting inflicted with the status.