Ogres are the evolved forms of Goblins. They are humanoid monsters with varied intelligence, around as smart as a human three year old. Their stats generally favour attack power over speed, though some individuals are capable of magic. They move around in groups and rarely leave their territories.
Oni: Unique species, raises Taboo upon evolving. Has a human-like appearance 
According to Wrath the most notable differences in Ogre's evolutions are the sizes. With each evolution, the size of the individual increases. If the individual chooses to evolve into an Oni from Ogre General, the individual will decrease in size, but gain considerable power.
Ogre King Monster file
A unique ogre that appeared at the northwest edge of the Renxandt Empire. Also known as the Sword Demon. It has a preciously unheard-of skill that allows it to produce magic swords, which allows it to defeat many adventurers single-handedly, causing huge losses. Though it's difficult to tell from the giant size of the ogre and its skill with magic swords in close combat, its magic scats are actually higher, since producing magic swords uses a great deal of MP. Since it has defeated so many humans. which afford higher experience points than monsters, its level and stats have grown much faster than its skills. The empire later assessed its danger level as a high A.