Combined, the three games have more than 70 million registered players and have topped $1 billion in revenue -- but it's hard to know exactly how much of that Hearthstone is responsible for. As of May, Hearthstone had topped 30 million players.
According to SuperData, Hearthstone "dominates" the digital card game genre. That $20 million is thanks in part to its release on smartphones earlier this year; SuperData says that monthly revenue increased 31 percent following that.
Without getting into any specifics, Activision Blizzard suggested earlier this month that the release on new platforms (and availability of new content) helped to almost double Hearthstone's "key engagement metrics" as compared with the year prior, when they were "already very strong."
Hearthstone is a free-to-play game where players can spend money on things like card packs and new content. Initially, the latter took the form of expansions like Naxxramas, but more recently Blizzard began selling new (cosmetic) heroes.
Hearthstone's next expansion The Grand Tournament is due out later this month and brings with it 132 new cards, as well as a new game mechanic.