Here is the full list of all 20 Interloper achievements.
Win a match in public multiplayer.
Complete the campaign.
Defeat the Expert AI on any map.
Defeat the Expert AI on every map.
Defeat the Expert AI on any map with the Motility Handicap.
Defeat the Expert AI on any map with the Fertility Handicap.
Defeat the Expert AI on any map with the Loyalty Handicap.
Defeat the Expert AI on any map with the Vitality Handicap.
Defeat the Expert AI on any map with the Hostility Handicap.
Defeat the Expert AI on any map with the Brutality Handicap.
Defeat the Expert AI on any map with the Prosperity Handicap.
Win 5 consecutive matches in public multiplayer.
Win 10 consecutive matches in public multiplayer.
Win 15 consecutive matches in public multiplayer.
Win 25 matches against expert AI or in public multiplayer.
Win 50 matches against expert AI or in public multiplayer.
Win 100 matches against expert AI or in public multiplayer.
Win 250 matches against expert AI or in public multiplayer.
Win 500 matches against expert AI or in public multiplayer.
Get a top-10 ranking in the leaderboards.