Shepherd, when asked to choose an ending, goes towards destroy. When shep gets on the destroy platform, shep faces the node, then turns around and starts walking. When shep reaches the edge of the citadel a tiny chrome reaper appears out of nowhere and turns into a surfboard. Shepherds whole body gets metalized, if she was female she turns into a man, and he uses the power to save the galaxy from the reapers. This still destroys the relays though.
Realizing that no one would accept him in this form, Shep flies away and lives on a different planet for a long time. Then one day a giant evil entity called galactus comes to try and destroy his world. Scared, he makes a pact to become its herald, searching for planets for galactus to consume in exchange for safety of his "home" world. Eventually he reaches earth, but was away for too long and didn't recognize it. Before he could make a horrible mistake, the fantastic four stop him from harming the earth, he destroys galactus, and they all live happily ever after.