As a 56 RDM soloing death from above is absolutely impossible. Your stoneskin will be shredded in one hit and without the AF fast cast enhancement you'd never get it up again. I have never been successful in putting it to sleep, either.
I would suspect that the absolute minimum for soloing it would be around level 69, and even then it would be a very long and risky fight. The reason I throw that level out is that it gives you a chance to reach the spawn point alive since most of the critters in that room won't aggro you. Even with a RDM and THF combo it took two runs at the room before we finally made the pedestal (the first run we killed half the mobs before we 2HRd it out of there, then went back in and cleaned up the rest) and the fight would have been rough without the renkei we made. I will probably be attempting to solo this soon for sport now that I've popped 71 and hitting it should be trivial.
Remember: this mob has a constant 100 fists effect on it when spawned ... your defences will be stripped fast. Even with a NIN sub your utse will be of no benefit since it will be stripped in less time than it took to cast it, and I've watched that ******* Pollen for over 2500 HP before ... with a sword and an extremely fast stun macro it is possible to solo it, but it will be **** difficult for a RDM under 70. After 70 you should have enough weapon skill to ensure that you can hit it and you at least have a fighting chance of winning.