I am bumping this topic on account that I actually
do have some real advice to give that has not been mentioned.
After being knocked off the platform an infuriating number of times myself, I began watching Moldorm's movements much more minutely, and noticed that there was a pattern to it that provided an excellent opening for attack. Based on what I learned in memorizing Moldorm's attack pattern, this is what I can tell you:
There is a distance you must estimate on the platform--you'll get a feel for just the right distance once you start observing this yourself. But pay special attention to this: when Moldorm has enough space to move, he will move straight in one direction for a few paces, but then always do a 360 turn after covering the same short distance each time, turning tail right there. Once you can estimate that distance with ease, position yourself so that Moldorm is coming directly at you from just beyond that distance. Despite the reflex you may have to get out of range, you must trust your observations and not move as Moldorm comes toward you, because if you have correctly estimated the distance, Moldorm will most certainly do its 360 turn the moment before reaching you, literally bringing his tail directly in front of you to hit. If you instead move back as Moldorm comes toward you, you'll be too far from the tail when Moldorm does his turn and miss the opportunity.
Now having said that, I have more to add: stay away from the left side of the platform, it's better not to attempt to hit Moldorm on that side. The reason for this is that Moldorm's attack pattern is disrupted every time he hits an edge, becoming irregular and unpredictable. Therefore if you are positioned near, you are in danger of suddenly being hit since he is no longer bound to his attack pattern at moments that this occurs. The left side of the platform has that hole in the center, and the narrow space surrounding it means that Moldorm will continuously be bouncing off the edges when on that side: thus, stay away.
In addition to the disruption of edges, you'll notice that when you're down to the last hit that must be landed on Moldorm, his movements will speed up and he will be harder to follow--I can't help you here because it didn't seem to me as though Moldorm was following the same attack pattern anymore. Once you're down to the last hit, you're going to have to try your luck and just land it.
Also,
I assure you you're not the only one bearing Moldorm a grudge. =P