by unlocking all achievements but you cant use it

U have to get 1000 gamer score
(i think)
try it i did and it worked but my friend did it and it did not work

and 1000 gamerscore in halo 3 only

my friend manny jammin57 he did all the piont on campaign and he got it and the security
helmet(the bumble bee head)

P.S. no u cant use the sword

the pionts achevments srry

u need the katana achievment
which is all achievments and gamerscore
unfortunately you can't use it