LUA SCRIPT (great for monitoring RNG3, the counter): https://pastebin.com/wURS8Qyr ROUTE CAN BE FOUND HERE: https://pastebin.com/vLGeQik8

The Basic Concept

In this game, if you save in front of a duel and soft reset, the only time that RNG is advancing at 60fps is on the "Continue Game" screen. RNG is frozen during the opening titles and during text boxes. RNG advances about once per second (technically 64 frames) while in the overworld. So, the basic idea of the route is to stack your deck, hit Continue Game frame-perfectly, wait on the overworld if necessary, and get turn 1/2 wins. The "Easy" Frame

Because of lag frames (where input isn't being read) while displaying the save file's data, there's a 4 frame window where you can hold A to enter your file. There's also one frame before this window where pressing A can enter your file, and of course every frame after the window. So, the best way to enter your file is not to mash, but to hold A during these lag frames.

Waiting

The once-per-second advancement is very odd, but what's even odder is that it runs on a global timer, which is going even while RNG is frozen. This is why when doing the Kristin booster manip, you have to delay exiting her text, so you have enough time to run to Heather. For waiting in manip, there's a particularly important detail: If you get into your file very quickly, RNG will advance almost immediately after:

So, if you feel that you were a bit slow getting past the Press Start screen and such, it'll take much closer to a full second to get one advancement:

To help with nailing this (and saving frames over all), I mash A and Start through the opening. If you're going for an Easy entry, be sure to mash A after file entry to initiate pre-duel dialogue ASAP, or you might get this advancement accidentally! Extra Notes

One of the odd things about RNG in this game is that when you soft reset, your starting RNG changes depending on your selected deck's contents. I pinpointed a few key cards that, despite never being used, when added to a deck, they 'increase' your soft reset RNG: DCE, and vending Raichu. Computer Search and Rocket's Sneak Attack also have this trait; they often get used, but sometimes they're just added for RNG purposes. (The "Water evolutions" filler being Water specifically in the Chip edit is simply because I have never had adding more Water types influence the RNG) I've also noticed slight variance on how many times RNG advances when you Continue Game. Very rarely, a "wait one second" could become "easy" or "wait 2 seconds" instead, because of RNG advancing one less/more time when loading. If you're sure you're hitting a duel but it just isn't working, try the adjacent options. Another thing is that the once-per-second RNG advancement won't happen on a lag frame. This is particularly noticeable in the Colorless Altar, which has a quite laggy room, and requires delays in its manip (other laggy rooms, like Bernard's room, just need an easy). The quick advancement is almost always skipped over; for consistency, it's best to slightly delay your file entry, missing the quick window entirely, and wait closer to a full second. (Fun fact: If you enter your file frame-perfectly, it might skip over the quick advancement AND the one afterwards, and you won't get an RNG advancement for over 2 seconds.)

Original work not done by Raagentreg