This assumes you know about executing the down+A glitch

The glitch behaves differently (runs a different memory location as if it were code) depending on the context of the duel. Executing it during a Whirlwind switch, with certain things setup (like temporary world map variables) will bring you to executing your deck's cards as code. A small deck edit sets up that code to trigger the credits cutscene

There are two main frames you can aim for, one from the tutorial RNG, and one from soft reset RNG. Hitting the frame from tutorial is much harder due to more human input variance, but it should theoretically be 3 or 4 seconds faster. (Less wait time, no saving in diary, but he plays a Bill during his turn)

If you just want a time instead of 1st try [highly recommended], do the soft reset, because you can re-attempt it over and over quickly.

details are here (and of course, you should watch the run too): https://pastebin.com/csRih4Wj

oh also Flowtimer is here https://gunnermaniac.com/ft

Original work not done by Raagentreg