He's difficult but by no means impossible. It can't be stressed enough that you need [i]three capable shooters[/i] to take him down. If there is a weak link in your fireteam, you're in for a frustrating time. 365 damage weapons of the appropriate burn. You've got to keep him staggered, so sniper rifles or machine gun crits are, well, critical. My team used three 365 Corrective Measures. We had much better luck with them than void snipers. Melted him to half health with weapons of light and then started running laps around the arena while dismantling mines. Don't get greedy. If Skolas is up in your grill and he's "almost dead!", stop shooting and run another lap or two. Hope that helps.