This guy is NOT to be taken lightly. I am not 100% sure, but at least 90% sure that you absolutely MUST have a crapload of BLM's that know how to cast in sync. Spent about 10 hours working on Reverend Mails. First 4 runs went allright, we had 2 party's of blm's. Then my run everything fell apart, people left.
Reformed in Whitegate, couldn't get many blm's, so we just stuck with other DD. Had 3 blm's and 2 rdm's (sleep duty's on ele's). First run (mine, again), total failure, it was quite nasty, but we gave a good fight. We re-strategized our Skillchains and Magic Bursts, and went again.
We then had a 2 HOUR EPIC BATTLE that might have been the most fun fight I have ever had in my 3 years of gaming. Just so ya know, after the first 20 mins or so (if you can't kill him in 45 seconds which you probably can't w/o 5+ blms) he only comes out of his shell for maaaaybe 15 seconds at a time, and regens at least 15% of his health each time he goes in his shell. Elementals CAN build up a resistance to sleep, but after 2 HOURS our rdm's were still sleeping them just fine. It was an EPIC battle with a Hurculean effort, we had him down to 15% once, but never that close again. We conceded defeat after much laughter and hurrahs.
Was so entertaining, that one of our Mele's told us he was planning on quitting, but the fun he had at this battle convinced him there is still fun to be had.