Soloing Hakkar is simple as a retribution paladin. First, let me start by saying that I kill 4 out of the 5 priests. Tiger, Panther, Snake, and Spider bosses are all easily solo-able. The fifth boss, the 'bat boss', if you will, is difficult for me because I cannot interrupt her heals. Without any form of mana drain, I just don't consider this do-able as ret.
By leaving the bat boss up only, Hakkar has a nice little silencing ability, but that's very insignificant. Everything he throws at me is so minor in damage that I just let seal of light, divine storm and judging of light do my dirty work.
When approaching Hakkar, it is not necessary to kill any of the mobs. You can easily avoid the pats, and all I do is run straight up to the top where he is waiting and I charge right at him, turning him around so that my back is to the small structure behind him. None of the mobs will aggro while fighting him.
Buffs are as follows: Seal of Light, Blessing of Might, Retribution Aura, Judgement: Light.
FCFS rotation applies, with Consecrate as optional. I tend not to use it to keep mana high.
This is really just a DPS race, and as ret I have no problems. Hitting Avenging Wrath as soon as I engage, he usually only gets four phases of his siphon life in before he is dead. All of his abilities are non-factors here, and the siphon life is negligible. Because there is only one target to drain life from, his HP barely goes back up.
I wish this could be more detailed, but like Onyxia, this is an extremely easy fight. Just stay put in your spot at the top of the platform and he'll be down in minutes.
Khor