Castle Crashers/WMG

The Painter has a grudge against/obsession with the Orange Princess
This would explain a great deal; Why there are pictures of her dead in its boss chamber, what the Painter's doing teaming up with the Wizard, and why the Wizard took along the Princess from the Industrial Castle instead of just leaving her there.

The Cyclops and the Groom weren't really evil.
Apart from the Cyclops's magma fortress and the sinister conehead helmets the Groom and his knights wear, there really isn't much evidence for them being bad guys. The Cyclops had no idea that the bride he was purchasing from the Theives had been kidnapped. Cyclopses aren't known for being too bright; he was probably just happy that he'd found someone for his best mate to marry. For all the Groom knows, you're trying to kidnap HIS bride-to-be. When you kill him, the Cyclops finds his dead body. Does he attack you in revenge? Nope, he runs out of the church crying; he seems SCARED of you. You later find him holding a funeral for his poor deceased pal. Does this seem like remotely evil behavior? One final thing that clinches it; when you defeat the undead Groom and Cyclops near the end of the game, their souls pop out of their bodies and ascend to heaven. No other boss does this, proof that among the villains of Castle Crashers, these were just two guys who made an honest mistake.
 * Supported by Castle Crashing a Wedding.

The Orange, Red, Blue and Green Knights are the second team of knights
The Blacksmith was the Purple Knight, as evidenced by the fact that he would appear to have a purple cross on his chest. The King was The Gold Knight, was the eldest, and eventually became The King. the Nurse in the Animal Ark was the Pink Knight, because you gotta have a token girl. and, of course, the Necromancer was The Black Knight, who was always unstable, and eventually either betrayed the other knights and joined up with The Wizard or died and then was resurrected by The Wizard and forced into working for him against his will, thereby driving the others to retire and pass on their duties of basically being super heroes onto the next group of people, and the party at the beginning of the game was the celebration of The Red, Orange, Blue, and Green Knights becoming the new protectors of the kingdom.
 * Confirmed in the case of the Blacksmith having been a Castle Crasher once: he's become available through DLC as the Purple Knight.

The Orange Princess was killed somewhere along the line.
When confronting The Painter, there are assorted pictures in the background of surreal things. However, the one that seems to pop up the most sticks out; The Orange Princess with a knife in her back. Either he's obsessively drawing about doing something particularly nasty to her until you show up, or he's letting slip a plot by the Wizard in case the original plan fails. One last "Screw you" to the knights to let them know in some way they also failed.

The Green Knight is a skunk.
The white stripe on his helmet, his character portrait with the stink lines, his magic appears to be stink, and you never get to see what he looks like without the helmet.