Quote Originally Posted by Jolts
What about the glob of mako that magically stayed around his body?
When Mako condenses, it becomes Materia. Basically, Sephiroth was suspended in a semi-solid blob of congealed Mako - not quite solid, since Cloud was able to reach through it, but substantial enough to contain Sephiroth.
See, he was conscious, I think. At least a little bit. That, or Jenova did all that before you actually get there.
That's the general understanding - that Sephiroth was conscious, but immobile; able to exert his superhuman will through the Lifestream, which is pretty plausible since he was practically in the Lifestream, which is a powerful flow of spiritual energy - the same stuff that forms the human consciousness.