These guys are tough, really tough. Thankfully, they aren't random encounters in the first Grand Staff... This is not true for the Second Grand Staff, however. You can find them inside Grand Staff's armory, in glass pods. You can examine the pods to engage these guys in battle. Don't do so unless you are at least level 44 and have some kick ass skills, weapons, rings, and spells though. The mixture of Mindus and Shadowus is absolutely Classic. Not only that, the creatures have nearly 12,000 HP, and will automatically restore ~700HP per turn. So you need to ask yourself, can you do enough damage to kill these guys? Keep in mind that they do not have any elemental weaknesses, and their physical defense is unrivaled. You won't be hitting these guys for half as much as you would a normal enemy