For P3 there's no reason to use the shield if you have assigned healers. Using the shield will make your dot fall off if you are unlucky or didn't conserve energy to start.

As a dps all you have to do is:
- make a macro "/castsequence reset=combat Revivify,Flame Spike,Flame Spike,Engulf in Flames" and tie it to a key (not from the main bar as this one will be overwritten).
- target Malygos
- make sure auto self cast is on in interface/combat
- spam that button!

As a healer:
- target yourself
- build combo points on yourself (4-5)
- use the big heal

As a raid:
- group up close together
- move whenever one of those electrical cloud things is on the raid (make sure you all stay together)
- stay 30 yards away from Maly but no more then 60

For 10 man you should need 2 healers, for 25 5 healers can easily do it or even 4.

As dps you could also leave out the revivify, which would increase dps, but will also remove a small safety. It will stack the dot every 8 seconds instead of every 9. (/castsequence reset=combat Flame Spike,Flame Spike,Engulf in Flames)

As a boxer this should be somewhat easier as well cause you don't have to worry much about what buttons to push, just spam one and keep your drakes together.