Warhammer 40,000: Space Marine 2

Any PvP match you win counts, including ones joined in progress which is how I got mine. There are only three game modes for PvP (more might get released later) but I recommend playing Annihilation (team deathmatch) due to it being an easier game mode to burn through. Whichever you choose remember that there are achievements to play all the modes at least 10 times so losing still makes progress in other areas.