For a 10 man raid against lethon I would suggest you bring:
1 TANK preferably tankaadin(prompt palladin)
1 Healer Preferably Healadinn
4 Spell casters such as magi or warlocks magi prefered
4 mele dps we did 2 dks and 2 wars
for 2 man only bring 2 casters and 1 melee dps

First you must know if u die do not go into battle all it will result in is broken armor wait for the de buff to come off!

If you do it right your heal din will only have to focus on your tank din.

First have the tank kite Lethon to the portal so lethon has his back to it then the mele dps should attack at his side that is not shooting the shadow bolts (the sides switch half way in)this way the tail do not knock u back the casters should stay behind the tank as far back as possible
when lethon uses his ability that knocks u out and brings a soul out of you the dps should wipe them out ASAP for they heal the giant beast and as long as you stick to that you should be done in no time

Also the healer should be same level if not higher than the tank