@justadude.
Endowment does not work in my opinion, as no spirit actually has immunity to normal weapons as a power, they only have materialization, which grants the spirit immunity to normal weapons when he is materialized. So IMO the spirit can only endow "materialization" to you, which is absolutely useless for a physical being. I take the endowment power literally: meaning power for me is what is listed under "powers" or "optional powers" in the critter stats.
Okay, look at SR4A, p186, under Spirit Combat.
Physical spirits have the power of Immunity to Normal Weapons...
Pretty cut and dry, really. Now lets look at SM, p 99, under the Endowment power.
The spirit grants the use of one of its powers to the subject.
Please take note that the entry does
not say anything resembling "
one of the powers listed in its Critter entry..." All it states is that it grants "
one of its powers". Yeah, I'll grant you that the spirit would have to Materialize before it can grant Immunity to Normal Weapons, but once it's Materialized then it
has ItNW, and can grant it via Endowment. No room for ambiguity.
Basically, Hellfire, you aren't taking Endowment literally
at all. You're creating a whole new restriction based on trying to force the power to work in a way that aligns with your preconceived notion of how it
should work.
If
you want to House Rule that it
doesn't work at
your table then feel free, if you're GM then your rules go after all, but according to strict interpretation of RAW, it does indeed work.