This is actually a test encounter on a single server from what I understand so it’s a very new addition

I severely doubt that this is the answer but 2+3=5 and Sombra is supposed to be the 23rd hero. My best guess is that there's some mathematical clue people aren't seeing etc.

Haha the other day my team got into a 6v6 Genji battle. 12 cyborg ninjas running around on King’s Row. It was ridiculous and honestly super fun