Well, in this case it's more like "finding a killscreen in an endless game with a TAS", but I figure it's close enough to go here...
One A2600 game I have been testing for suitability for submission is an unreleased game named
Telepathy, which was originally created by Atari to be played with an experimental "MindLink" controller (control your Atari
with your mind by spastically twitching your face!) However, the existing prototype is fully playable (and thus potentially TASable in BizHawk) with a standard A2600 joystick.
The game was generally presumed to be endless when I started a test run a couple months back, mostly to determine where a potential submission would have to stop (leaving aside the question of whether a game like this could even be accepted on the grounds it is technically not a finished game). However, upon reaching the 11th level of the game, I found a certain obstacle could not be passed even with tool-assistance if it was already active when you appear on the screen it was on.
I reported this by email to another A2600 enthusiast (who runs
a fan website with all kinds of information on the console and its games), and after some back and forth trial and error between us discovered that the seemingly impossible obstacle could be passed if it wasn't active (that bit requires luck manipulation), but the final section of the same 11th level was impossible to beat because you aren't given enough time on the death timer to get through it. Thus, a killscreen was discovered! :D
Details about the above discoveries for anyone interested in reading
