Here is the full list of all 12 Castle Crashers achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Collect all the animal orbs.
Survive until 2:30 in a Back Off Barbarian match.
Win 40 Arena Online Matches.
In a 4 player game, resuscitate each of your fallen comrades at least once.
Collect all 4 princesses' kisses in a multiplayer game.
Complete the game using any character.
Defeat any boss by playing one of his own minions.
Navigate the Abandoned Mill without hitting any obstacles.
Find and dig up ten buried items.
Complete the Home Castle through Barbarian Boss areas without attacking any foes.
Defeat any end boss without using any magic.
Using a catapult, fling a knight with maximum power.