Following some big announcements at BlizzCon earlier this month, Blizzard has kicked off a Heroes of the Storm promotion that provides some excellent incentives to play over the next seven weeks or so. The Nexus Challenge, as it's called, rewards you for playing the game with friends. Between now and January 4, playing 15 games with at least one friend in your party will land you Zarya for free, as well as an Oni Genji portrait. These games can be played in Co-op Vs. AI, Quick Match, Unranked Draft, or Ranked modes (which most notably leaves out Brawls).
Doing so also earns you some rewards in Overwatch: an Oni Genji skin (above), portrait, and spray. If you play that game on consoles (HotS is PC-only), you can connect your Xbox Live or PSN accounts to receive those rewards on Xbox One or PS4.
Even better rewards await those who play 15 more games. You'll receive four additional characters: Auriel, Greymane, Kerrigan, and Li-Ming--in addition to the Orochi Hovercycle mount and a 30-day stimpack. That would all cost a fair bit of gold or real-world money to buy otherwise. New content is on the way to the game including two Warcraft characters and a variety of holiday-themed skins.