unlike other halos, there isn't a matchmaker for campaigns in ODST.
beaten
(original xbox)halo-legendary
halo 3-legendary
halo reach- legendary
need the vidmasters and ODST co-op/firefight.
missing:
Annual, Brainpan, Endure, Deja Vu, Marathon Man, Audiophile
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Endure is a really easy achievement if no one lags out. The rest are pretty easy as well. I haven't played ODST in years, but I don't mind helping you with one or two.