Pokemon Red/Blue on GameBoy...the duplicate item trick
To get WELL 99 of an item, put the item you want duplicated in the sixth item slot. Make sure you have the Fly HM, then Fly to Viridian City. Talk to the old man that stopped you in the begining of the game( kind of to the north) When he asks if you are in a hurry, say no and watch him catch a weedle.
Then Fly to Cinnabar Island, and use the SURF HM. Surf along the right COAST, Not in the water, if you surf in the water it won't work.
Now, use SURF until you run into a Pokemon called ''M'', ''Missingno.'', Or a Pokemon over level 100 Once you see one of those, kill it or just simply run away. DON'T CATCH THE M OR MISSINGNO. AS IT WILL RUIN YOUR GAME!!!
When fighting a high level M if you have a slow pokemon and it attacks you are screwed, as it has a VERY high attack, you can beat him by simply using a quick attack.
after you win/run look at your sixth item it should look VERY weird with wird symbols and such, don't worry all it means is you have over 99 once you use it up alot it will stop using symbols and once the supply gets back to 99 it will show up as ''99''