It's pretty wild that over its decade-long life, Hearthstone hasn't done any major crossovers with other Blizzard games. Obviously it's based on the Warcraft universe, but given the liberties taken with that source material (the current expansion involves launching spaceships) it's a surprise that we haven't seen any significant team-ups.
That changes next January, with the launch of the Heroes of Starcraft mini-set. Aside from fitting perfectly with the current interstellar theme, Blizzard promised it includes as many iconic units as possible.
Cards will be marked with an icon that designates their Terran, Protoss or Zerg affiliation, but will be playable across multiple classes.
No surprise that the Zerg go for all-out aggro, while the Protoss is focused on mana cheating high-cost cards, and the Terrans will be able to build and launch Battleships.
Each faction is led by a Hero card, meaning that when played it replaces your current hero power. I'd be amazed if these aren't extremely flavourful and equally OP.