Last month, Slay the Spire 2’s Act 3 boss Doormaker – the third in a series of late-game reworks – was removed and replaced by Aeonglass. Now, developer Mega Crit has revealed how its fun visual design came to be.

Slay the Spire 2 is now in the middle of its early access journey, and developer Mega Crit has a pretty solid cadence of updates, many of which have reworked and even removed bosses in an attempt to perfect the roguelike deckbuilder’s gameplay loop and level of challenge. Act 3 is one part of the game that’s already had four different bosses, and while we don’t know for sure if Aeonglass will make it to 1.0, its hourglass-inspired design is among the game’s most visually arresting yet.

In a recent Steam blog post, Mega Crit animator Chris Gortz explained the team explored different concepts following Doormaker, “including a multi-faceted pillar of death that could rotate its sections to reveal different capabilities”. Such concepts were apparently envisioned as an upgrade of Doormaker’s ‘rocky portal’ design, but the team eventually moved away from that.

The post reveals five different Aeonglass designs – all different takes on the concept of a killer hourglass – with option B emerging victorious after some debate. “I did some tests to make sure I could simulate 3D rotating metal rings in 2D space. The result wasn’t much to look at, but as a proof of concept it worked well enough for us to move ahead,” Gortz explained. To figure out its combat style, doodles helped, and the concept of “a big atom” with blast and slice attacks took form.

Art director Marlowe Dobbe also “requested that the stuff in the hourglass move more like lava lamp goo than the traditional sand”, which pushed Gortz to use the same smoke shader as for the body of the Living Smog boss. The end result is very effective.

The most recent beta patch has already nerfed Aeonglass’ front-loaded damage and swapped some of its animations, so expect more changes to hit the Act 3 boss in the future even if they stick around.

Slay the Spire 2 isn’t expected to exit Steam early access until 2027 at the earliest, as the first game took one-and-a-half-years to fully flesh out. Console releases haven’t been confirmed but should be expected around the time of its eventual 1.0 update.

Eurogamer’s early access review of Slay the Spire 2 noted that “Mega Crit demonstrates that it absolutely understands what makes this eccentric card game crackle and fizz, and why so many people enjoy playing it.”