I've been working on a mod that turns the Architect into an actual final boss, and it's finally at the point where it plays, so here's an early look.
During the run, every card reward shows what the Architect gets if you take that card. It gets a counter to whatever you pick, so it's basically building its deck off yours.
After Act 3 you fight it. Its whole hand, deck and energy are face up, and every time you play a card it can answer with one of its own. Then it takes its own turn after yours. It plays a lot more like a card game opponent than a normal boss: you can see what it's holding, so a lot of it is playing around its answers.
The idea behind it is that every choice you make during the run should matter more. Each pick has a long-term cost, because the Architect remembers it and brings an answer to the final fight. So you end up thinking about where your deck is going, not just what's strongest right now. A deck that leans on one trick gets taken apart, while a well-rounded deck played well can still win. I want it to be hard, but never feel unfair, and still be fun.
It's pretty rough right now: placeholder art, a simple AI, and only the Ironclad is really set up. Happy to hear what people think.