Ive done the encounter like 5 time now, We find the best trick to kill Anon, is to poison field, as long as he is poisoned he cant heal as much as he would like to and we can be killed a bit faster.
About going into Earth ele form and leeching life I didnt know about that, I dont really think he leeches life, its more like he has really incredibly high HP regen, he is a mage not a warrior... But I can be mistaken. Its true we have had him at 28% and in a matter of 3 sec, he has gone up to 40%.....
A good team of mixed templates is needed, and true that you need to set some people just to fight the boss, some to kill spawn and other just to Crossheal all other members to keep everyone alive.
Its a very hard and fun encounter, but it can be very tidious and time consuming, The first run, from starting the quests for the rooms and killing the boss, took us 18,5 Hours, as we didnt know what to do and stuff. Now all rooms and boss can be done in a fast manner in less than 3 hours.