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.
Complete the Home Castle through Barbarian Boss areas without attacking any foes.
Collect all 4 princesses' kisses in a multiplayer game.
Using a catapult, fling a knight with maximum power.
Defeat any boss by playing one of his own minions.
Complete the game using any character.
Find and dig up ten buried items.
Defeat any end boss without using any magic.
In a 4 player game, resuscitate each of your fallen comrades at least once.
Navigate the Abandoned Mill without hitting any obstacles.
Win 40 Arena Online Matches.
Survive until 2:30 in a Back Off Barbarian match.