Help with Boss in Third Level of Numa Prime: Yell

[Doubletime]

So what is the strategy with this boss? He nuked our party of 3 operatives and 2 commandos pretty easily. He seems to dodge all direct attacks. It appeared that he only took damage from explosions, from the oil maybe. But I have no real idea how the oil was igniting or if that was even it.

Anyone want to give me the scoop?

Edit:

After a couple goes at this boss it appears that lighting the oil slicks in the area by shooting the floating laterns can ignite the boss and do a good deal of damage. Same approach with the Guardian. Makes the kill go a good bit faster.

[Doubletime]

Well I suppose there is a better way, but we pure group dps seems to work eventually.