Beat the endless dragon when it had 25AC using the Warrior, Play in Browser mode and the screen went black.
Hmm, I'm having trouble duplicating this bug. If you'd like, you can email over some more specific info at dev@pixelflightgames.com to log the bug report. I know you said you're playing in browser mode, but are you playing on a phone or pc? When the screen went black could you still hear sounds/music? There is an autosave function, if you reload and hit continue run, did it take you back one wave to the boss fight, or did it load the next stage correctly? If you'd like to email this info and anything else you think could help, I'll take a closer look! I'm glad you're enjoying it, and thanks for helping to make the game better!