Castle Crashers is a 2D beat 'em up video game independently developed by The Behemoth and published by Microsoft Game Studios. It features music created by members of Newgrounds. The Xbox 360 version was released on August 27, 2008 via Xbox Live Arcade as part of the Xbox Live Summer of Arcade. The PlayStation 3 version was released in North America on August 31, 2010 and November 3, 2010 in Europe via the PlayStation Network. A Microsoft Windows version exclusive to Steam was announced on August 16, 2012. The game is set in a fictional medieval universe in which a dark wizard steals a mystical gem and captures several princesses. Four knights are charged by the king to rescue the princesses, recover the jewel, and bring the wizard to justice.

The game supports cooperative gameplay for up to four players, either locally or online. The game progression in terms of what stages are unlocked is defined by the hosting player; however, each player character will gain experience points and acquire wealth, weapons, and animal orbs independently as they progress with the rest of the party. In each stage, the player can use melee and combination attacks. Each character has a unique magical ability in order to defeat foes and a health meter that, if drained from enemy attacks, will cause the character to fall in battle. In single player mode, this ends the stage; however, in cooperative multiplayer other players may attempt to revive the downed character.
Basically just damage enemies to get EXP to level up, and stuff. Find weapons, pets, etc.

I've been play this for hours on end with my friends, and it is just SO FUN. All the weapon choices and pets... I love the sandwich too! I usually play the red knight since I still haven't unlocked the next knight.

I've unlocked a few people. I have the White Knight (ha) and got to level 34 I think.

If you go to the Industrial Castle, kill the giant hand and the shooters that come down over the red tiles, you can then toss your Boomerang to where it hits the electric tubes that pop up and constantly hits it where it doesn't return and if you repeat it, it levels you up one time each time you play through.

Next, also have the pet Giraffe and it helps level you up faster. You normally can get between 1600 to 2000 EXP each time.