When you want an endless mode but there isn't an endless mode - create your own. The Emperor would be proud.

A fast way to farm kills represents the campaign mission Skyfire.

- Start a new campaign and choose the lowest difficulty level. You want your 'nids as squishy as possible.

- Skip the tutorial level. You are a proper Angel of Death by now.

- Continue through the Skyfire campaign mission until you reach the part where you have to defend the location until the door mechanism opens. This will be your farming spot for the next few hours.

- Load the checkpoint when you are tired of mowing through the swarm. A Space Marine needs a fresh start every now and then.

- Revel in the slaughter until the Kommissar declares that you are "Still a True Son of the Emperor".

May the odds be ever in your favour.