There are three arenas with seven challenges each. The first arena unlocks after Chapter 3, the others unlock after Chapter 9 and 12. Talk to Brock on the ship and complete any of the available arena challenges to unlock this achievement. Complete all 21 challenges to unlock this achievement.
- Take your time. These challenges have no time limit.
- These vary in task and difficulty, so level up and try again later if you're having trouble. Use a maxed out Skylander if you have one.
- You can only use one Skylander per challenge, so if you get knocked out, you'll need to retry.
- Between waves of enemies, the audience will toss out food. If you don't need it, leave it on the ground.
- Pick a target and stick to it until it's defeated, whether it's a small enemy or large one.
- Most of these are pretty simple. The only challenging ones are the last of each arena, where you have only 1HP.
The IGN Wiki has a good listing of the 21 arena challenges and their rewards: http://www.ign.com/wikis/skylanders-...ena_Challenges
Here is a video playlist by PlayWithPetey showing all of the arena challenges: http://www.youtube.com/playlist?list...u12h6YedQ5KA9x