Week 1
5 games with a friend gets you both the Oni Genji skin in Overwatch and the Orochi Hovercycle Mount in Heroes, plus sprays, banners and a portrait.
Week 2
5 games with a friend gets you both the Officer D.Va skin in Overwatch and the Busan Police Hovercycle mount in Heroes.
Week 3
5 games with a friend gets you both D.Va sprays and portraits in each game, plus the Overwatch Nexagon mount in Heroes.
Week 4
5 games with a friend gets you 10 Loot Boxes in Overwatch and 10 Loot Chests in Heroes.