On Steam, it's near 500 hours, but I've also played the Switch and mobile versions a fair bit.
I've beaten A20 Heart on Ironclad (with a status generating Fire Breathing deck no less!) and Watcher (with a stance dancing deck) but I'm struggling with Silent and Defect. There was one deck I had with the Silent where I had 2 x Grand Finale, and I had done really well with my card removes so most of my cards could draw and I had loads of deck manipulation cards like 3 x Prepared+, 2 x Acrobatics+, 3 x Backflips, some Calculated Gambles, I destroyed the A20 bosses with four potions left without taking damage... then realised I didn't pick up the red key with the last rest site. I'm sure that deck would have destroyed Heart.
Amazing, thank you!