Complete Monster: Rhade. Where do you even begin with this guy? All the other villains in the story claim to do their deeds for the good of the kingdom/empire. But this guy pretty much does all he does because he can. From the first moment Magnus meets him, even though they're on the same side he condescends to him constantly, despite Magnus having saved his life earlier (Rhade actually complained about Magnus not being fast enough), and then kills an unarmed old man as soon as he leaves the room. Then he punches you out when you try to defend a rebel leader which begins the downfall of Yumil as Rhade's the one who shows him only power can change things. THEN he forces slaves from the west to be drafted into the war by holding their own families hostage, and saying that it's YOUR fault for dragging them into the war! Quite frankly, it feels awesome when you finally get to stick a sword in his gullet (Or see it, depending on your alignment).
Game Breaker: The Item Duplication Glitch. It's a method that allows you to create up to 99 of any usable item. To which you can duplicate stat upgrade items, alignment upgrade items, even Champion Statuettes!
Ho Yay: Any scene featuring Yumil and Magnus if full of this. Like Yumil asking Magnus to "become his knight".
Grappers, as they hit hard no matter where in the formation they are, and always come in groups of 3 or 4. Thankfully you only face them in a few levels and you can get one.
Faeries and Gremlins, as they're Fragile Speedster incarnate and will dodge your attacks half the time. They only get real bad when paired with a healer at least.
Cockatrices can petrify you and the cure for that is not cheap. Also, on your side it robs you of experience as petrified enemies don't give any. At least you can upgrade your Golems into Stone Golems thanks to them.
Magnificent Bastard: The Glendale brothers, but Baldwin tends to be more bastard and Richard is more magnificent.