A few seasons after we thought we'd seen the back of one of Hearthstone's most divisive cards, he's back. And this time Dr. Boom isn't just a card, he's a whole expansion. Welcome to Boomsday.

As befits a set of cards themed around a mad genius, Boomsday looks to have the potential to shake the game up. That's a bit of a surprise after a couple of expansions that seemed to be more about consolidation than revolution. But it does mean players will have a bunch of cool new toys to play with.

Mechs are back in a big way, along with the "magnetic" keyword. This stacks mechs, combining stats and effects into one mega mech. At first glance this looks like a win-more mechanic. But it's also very vulnerable to Silence and hard removal, so if it takes off expect to see a lot more of that in the meta.

Omega cards aren't so much a new mechanic as a class of cards. They're ordinary, cheap spells which gain a much more powerful effect if their player has ten mana crystals. This seems calculated to maintain the slight skew in the current meta toward slower decks.

It's a similar story with the last novel group, projects. These are spells that affect both players equally. The idea is to build a deck that makes more of that effect than your opponent is likely to. Looks to have a lot of promise for some novel decks.

Boomsday is out on 7th August (not 16th June, as the literati might expect). Until then, here's a preview of some of the new content.

Want more? Check out our 22 other Hearthstone: Heroes of Warcraft features!