Complete the game using any character
For this achievement, you have to finish the game using any characters (knights or unlocked characters). Here's some general tips if you get stuck at all.
1. An easy way to hit enemies but make it difficult for them to hit you is by jumping and then alternating the X and Y buttons while hitting someone. This will keep you in the air, while you juggle their body.
2. Always have 5 health potions and 4 bologna sandwhiches on you at all times. They come in handy.
3. Keep in mind that all online play transfers to single player, so if you're stuck on a boss, host a game and play against the boss with a friend.