now here is the hillarious part,

1st time i did siamat on HC i one shotted him, i was perplexed how did this happen...

2nd i did him i whiped so many times i got respawns and left.

what post above says, you die due to hard to see clouds thingies not because of adds chain light or boss aoe.

move your char out of anything that looks like swirly clouds, they are not obvious.

after this i one shot him all the time.

IF you have low dps killing the chain light adds works wonders, but again avoiding clouds is the trick.

if you have a priest or druid just rolling aoe heals Circle of healing or Wild Growth should be enough at any gear lvl, the odd heal on a tank might be needed if you run anything but a paladin.