Oh, I've done my share of Pokemon-Myth-Busting.
- "Catch all 150 Pokemon, talk to Prof. Oak and he gives you Mew"
Nope. All he says is "Wow! Great job!" (more or less) and stares at you blankly. GameFreak gives you... a diploma that has absolutely no value.
- "Use Strength to move that truck in SS. Anne to find Mew"
Nope. Apparently that truck has its parking brake up. It won't budge. Ever. Nothing underneath.
- "Catch Missingno. and the game crashes"
No. Depends on the Missingno. variant. I caught my favorite variant (Kabutops Fossil) and my Yellow is still alive. That awesome sprite wasn't retained, but it's still a Missingno..
- "Catch all 250 Pokemon, talk to Prof. Oak, and he gives you Celebi"
Heard that one before. Just like in Generation I, all he says is "Congratulations" and that's it.
- "Breed a level 30 female Abra with Everstone with a male Meganium to get a Celebi Egg"
That's stupid. Results: level 5 Abra. Yay?
- "Take 6 Unowns to the Ilex Forest Shrine. The Unowns must spell CELEBI for it to appear"
... Nope. Doing that will just get you a team of worthless letters.
- "Stand in front of Ilex Forest Shrine for 8 hours for Celebi to appear"
Nope. Had my Gold on in front of that shrine for 8 hours while I did some... productive stuff on HG. Results: my guy just stared at that shrine for 8 hours straight like a vegetable.
- "Catch all 200 Pokemon, go to Mossdeep Space Station to go into space and catch Jirachi"
Lots of things wrong with that. Why would Jirachi be in space? I talked to everyone in that space station. All I got was... a Sun Stone.
When all else fails, nothing beats a swift whack upside the head.