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