"shrug". Well either way, thats the best thing Kain can do at this point. For all his variety, he can either just escape the metroid, mind control it or freeze it in time. He cant actually kill it if its got no soul energy.
A lot of the assumptions behind what "life force" is however is just that. Its either soul, or not. Both assumptions.
I doubt it freezes them forever, I think his only route would be escape... stalemate as long as the Metroid doesn't get anywhere near him and kill him with Phazon exposure, or phase through his attacks and drain him.
Metroids are... considered the ultimate life form, they are just different than anything else.
They consume life force because they were created as a predator to the most vicious parasite the galaxy has known, which apparently unless you're a Metroid, takes planet busting force to kill one. When exposed to radiation they absorb it and gain new abilities, when exposed to beta rays they speed up their own replication and growth, when Phazon is introduced they easily add it to their genetic makeup. Just introducing a Metroid DNA based Vaccine into Samus gave her the ability to absorb X on contact. In Metroid Prime if you read the space pirate logs it points out that they tried to control Prime and it would destroy and absorb their weapon systems and add it to it's own arsenal. Besides, if they could be mind controlled wouldn't the GF have already attempted to do it with their telepaths?
true enough, hopefully Other M will give us more insight. I seriously doubt that the game would create PIS for the Metroids though, they seem OP enough already.