This achievement is incredibly annoying, so prepare to restart the arena fight a lot of times.
This fight is like every other in the game, go to get an elemtn, get denied, fight one enemy, avoid traps and so on. I tried using Terrafin but his underground move is 10 seconds while the lasers start at 10 seconds and go on, plus you can't fight the enemies at the end while you're underground, plus there's a significant time delay between you pushing the button and Terrafin going underground. So you have 2 choices: get a co-op partner who fights the 3 enemies at the end while you stay underground and pop up when it's clear, only to go under or do it yourself.
I used Gill Grunt for the lasers and Spyro for the fight until the end. Because Gill Grunt's manuverability is second to none with the Water Jet Pack. The lasers themselves are fairly easy, for the most part they'll appear where you are. Some will attempt to block off any exit, as you're moving to avoid them they'll go from White to Red. Red is bad and if you keep your health high you'll notice if the bad lasers hit you.
For the final fight with all 3, you also get to avoid lasers. You have a choice of working it so they all die right after another. Which is to say focus on. Getting one low, move to the next until they're one hit away from K.O and then finish them all off in rapid succession. That strategy doesn't let the lasers get past the first firing.
Or kill everyone exxcept Hex. If you do it that way, you remove everyone else who will get in your face and knock you into a laser. Hex tho is long distance and if you are using a long distance character, especially Gill Grunt you can hammer away at her, dodge her attacks and worry about the lasers.
One other tip is if you get in a jam to remove the Skylander from the portal. I did this a few times, especially with the lasers that sweep in from the side and converge on the top and bottom. I was caught in the bottom after it had turned red and was about to get caught in a small box. I took the Skylander off, put another one on and it put me in the safe spot. Then again I played the entire game offline