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.
Survive until 2:30 in a Back Off Barbarian match.
Win 40 Arena Online Matches.
Collect all the animal orbs.
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.
Find and dig up ten buried items.
Using a catapult, fling a knight with maximum power.
Navigate the Abandoned Mill without hitting any obstacles.
Complete the Home Castle through Barbarian Boss areas without attacking any foes.
Defeat any end boss without using any magic.