Slay the Spire 2 developer Mega Crit has revealed the design process behind Aeonglass, the new Act 3 boss that replaced the recently removed Doormaker. The reveal offers fans a rare look behind the scenes as the studio continues to overhaul the early access roguelike deckbuilder's late-game bosses in pursuit of better balance and challenge, with Act 3 alone having now had four different bosses.

In a Steam blog post, animator Chris Gortz explained the team first explored concepts building on Doormaker's "rocky portal" design, including a rotating "pillar of death", before settling on an hourglass theme. Five Aeonglass designs were considered, with one dubbed "option B" chosen after testing 2D simulations of rotating metal rings; its "big atom" combat style combines blast and slice attacks, while art director Marlowe Dobbe asked for its contents to move like lava lamp goo rather than sand, achieved using the same smoke shader as the Living Smog boss. A recent beta patch has already nerfed Aeonglass' damage and altered its animations, and Slay the Spire 2 isn't expected to leave early access until 2027 at the earliest.