Thankfully, all those items are available at the game beginning, in Goldenrod Department Store.
What happens
The first program
Doing everything possible with just items is not a great idea, since we don't want going around the whole region just to get necessary items. A better solution is to make a simple program, which will write to a specified memory location, and jump to it afterwards. The first argument, controlled by the quantity of Potions, is the lower 4 bits of the byte I want to write. Quantity of Fresh Water controls the high 4 bits. Then the amount of X-Accuracies controls the least significant byte of the address to write, with the most significant one is always 0xDB. This allows me to write something more complicated to the (DB01-DB10) address range.
Because it saves time and items, the program exits in a wrong way, which will cause a very annoying side-effect: the menus will scroll the text like they were textboxes.
The second program
As soon as I deposit all the items in their respective places, I start writing the payload. Thankfully, the nearest place which allows the Coin Case to work is 4 steps from the PC. I optimized the withdraw/deposit combination so it would display the least amount of menus as possible (saves a lot of time, because of the side-effect mentioned above). Eventually, DB01 contains a sequence:
D6 12 21 FE DA 2C 2C 22 33 00 AF 3C 21 F6 12 E9
Or in assembly:
sub $12
ld hl,$dafe
inc l
inc l
ldi (hl),a
inc sp
nop
xor a
inc a
ld hl,12f6
jp hl
What the code does is takes the value set with the items (Potions and Fresh Waters), and subtracts 0x12 from it - this is to allow me to write values less than 0x10. Then it loads this value to $DA00, and returns control back to the game.
By swapping the last item (TM41) with Parlyz Heals, the code is modified to jump to the second part.
One of the bytes is skipped, and set to NOP, which does nothing. The problem is that DB0A is actually in the middle of the fifth party Pokémon data, and specifies if the Pokémon has any status problems. Setting it to anything but 0 would cause the addresses to change around, which would mess up the code.
Next, this program is delicately modified, so it writes a value to $DA01 - it only requires to change one byte.
The third program
The two last addresses need to be set to the same value - 00. To speed things up, I write a yet another program - which will replace parts of the previous one. I change the bytes at $DB03 to:
EA 22 DA EA A3 D8
Instead of writing one address at a time, this one writes two: $DA22 and $D8A3. This modification is entered and executed exactly like the previous one - by running around, changing the amounts of Fresh Waters and Potions.
Finally, I execute the final piece of code, and by going through the stairs in Goldenrod Pokemon Center... I end up on Mt. Silver. The game must be saved once more, because of the previously described side-effect, which causes the credits to require mashing A to go through. Saving and resetting gets rid of this effect, and after reloading the game, we can finally talk to Red and win the battle with him, without even fighting.
Special thanks to Sanqui, for discovering the actual arbitrary code part of the coin case glitch.
Noxxa: This movie displays a very impressive technical trick to glitch to the end using arbitrary code. However, during the first half of the movie, the gameplay is plagued by a significant amount of suboptimalities and sloppiness, and is clearly improvable in many areas, including overworld movement and item collection. Rejecting due to noticable suboptimality.
