It is inferred that he is the one behind the attempted Regicide of Claudia, the curse afflicting Fel VI, the current Emperor of Bafal, the pirate assault, and the Cultists of Saruin. His sister is Fel VI's wife, so if the emperor dies, he will be able to become Emperor himself.
During the event when the curse is lifted, you see a shadow that is the one who is casting the curse (Trying to break the Moonstone barrier projected) Neville throws a sword at his arm and stops the aggressor. When Cornelio comes to meet the king, Neville notices the wound matches that of the the one he attacked during that altercation with the curse. It is during that time he says that the Pirates that have been plaguing Melvir have been weakened due to internal strife, and wishes to crush them once and for all. the Emperor gives Cornelio the army to fight the pirates. At that time, the pirates are scheming in the Sewers, preparing to strike. During the pirate invasion, monsters also attack Melvir, who are being summoned by a Priest of Elore who is really a Priest of Saruin. The monsters summoned attack the castle, and the Protagonist drives the monsters off.
The ability to curse is perhaps the only reason why Cornelio didn't stop their activities in Melvir, either that or he stumbled upon the Cultists and wanted in on their ways to attain power to kill the Emperor and Usurp his position.