From the announcement (note: all references to "this Facebook post" refer to the Corvus Belli post about the contest, and not the TGN one. You can post your links on the TGN one, but your name won't go into the hat for the drawing!):
To participate, you just need to link your Halloween Mission Report in this Facebook post, or on Twitter using the hashtag #InfinityHalloweenMission Everyone who post a comment from October 25th to November 1st, will participate in the draw. We'll announce the winner next November 2nd. Good luck to everyone!