Singularity

Play 5 matches of Extermination. They do not have to be complete matches and you do not have to win them. Even if you jump in at the end it still counts.

Pretty simple. Just play 5 matches of Extermination. Make sure you click "Public Match>Extermination" because if you click "Quick Match" it may place you in a Creatures vs Soldiers match which will not count towards this. An Extermination match consists of 2 rounds. One round you will be the creatures and you must prevent the soldiers from activating the beacon. The other round you will be the soldiers you must eradicate the creatures by activating the beacon to eradicate them.

You do not have to win these 5 just play 5 complete matches. You can join in the middle of a match and play to the end and it will still count.

Grinding method -

If you own a turbo controller, an effortless way to get this and 100 matches is to go into the Extermination lobby, turn on turn R trigger, X, and A on turbo. This should cover all your bases for buttons you'll need to press. You cannot go idle in this game or you get kicked out. You do not need to mess with the control sticks.

Stay in the lobby, even if it's not full. Leave the box on, go to work, go to sleep, whatever. Eventually 6 people will fill the lobby and the game will start. You won't go idle and you'll keep on playing. Over time you'll get your 5 games, and eventually 100 games.