Safari Zone Trainer item toss glitch/toss key items/new unviable item underflow (Generation I)
Notes: While experimenting for different reasons, I came across something rather unique. It's a nice surprise because previously the only ways I was aware to get rid of key items outside of arbitrary code execution were things like to swap it in the roaming items and change maps, corrupt the inventory, or (if applicable?) item mutation/converting glitch Pokémon. This glitch actually lets you toss a key item as if you did it from the menu.
If you start a Trainer battle in Safari Zone mode (note: it seems you can't just change the mode in the middle of a battle, as I tried the participants glitch to do that and it wouldn't work; alternatively it might be because the foe would never flee and I had to choose run), then each time you throw a ball, the game will deduct x1 from your top item in your inventory even if it's a key item. If the stack is over, it will be removed and the item counter will become -1 as usual.
Additionally, although I haven't been able to pull it off without the memory editor arbitrary code execution program as a shortcut yet, this is theoretically another way of getting the expanded inventory; because if the item count is 0 it will underflow to 255, as if you did one of the other underflow methods (drink/fossil or dry underflow glitch). (I don't know what the Safari Zone-Trainer item toss glitch does to Cancels though/if it would work with a normally initialised empty inventory)
However, starting a Trainer battle in Safari Zone mode as it stands is relatively hard without arbitrary code execution and would typically involve already having the expanded inventory anyway (for namely the various text pointer manipulation exploits (also the glitch ooblg although there are no PCs in the Safari Zone except the out of bounds invisible PCs in the rest houses in Red/Blue(?)) so that would probably involve text pointer manipulation too) ; for those reasons I suppose this glitch probably isn't as useful as it sounds for underflow due to it being redundant?
As a small challenge I did a non-arbitrary code method. It would usually be easier but there were a lot of lag name items sadly, so you have to tap B while scrolling down until you can continue. Go to the TM37 item ball in the Safari Zone and come equipped with Master Ball x66. Find item 40, which should be a lag name/unterminated name glitch item called 4R u. Swap it in place with the Master Ball x66 stack, exit and press A on the item ball. Some glitch text should display, followed by a Team Rocket members's challenge text except it's an Erika fight. Now you should be able to throw Safari Balls at Erika's Pokémon. Once it flees, the top stack should have decreased by 1.
This glitch in essence doesn't have to be as complex as above though, as using cheat code 01C958D0 in the Safari Zone for instance will let you fight a Youngster there in Yellow; or you could set D058 with arbitrary code execution.
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