spent about 2 hours (2 full repairs) on this guy yesterday. my toons are ~3200-3500gs (dragon at 80-90k hp) with one being at 5000gs (122k hp)
I had no problem at all with the other bosses

What i've tried:
- 5 ruby: that seemed to work best, got him once down to 6%.
For some reason i always seem to get one of my toons dead early in fight. Probably because we can't use Evasion right away.
Apart from that, it's a game of attrition, and Eregos seems to outlast me at this point.
i spam the attack, and round robin the taunt+evasion.

- 4 ruby + dismounted healer:
my healer got hit for half his hp regularly, and died at the first phase shift. (a bubble i guess? how is that toon supposed to avoid them?)
Also the healer tried to follow the dragons and plummeted to his death once lol

- 1xruby 3xamber 1xemerald:
got the boss to ~15% with this group, but i have problem using the amber attacks correctly, and basically the main attack breaks the channeled one and therefore make it very weak.
I might try and macro a [nochanneling] somewhere in there.

Any other suggestions?
my fights take about 4min.