About the Yellow version thing. If you go north of Cerulean and go to the left of the bridge a little, you will see a patch of grass. Go right above the rightmost strip of grass, then save. Oh yeah! Make sure you have an Abra. Take one step down AND QUICKLY PRESS the START BUTTON! Now go to your Abra and teleport back to Cerulean. A little ! mark will appear above the other trainer's head. Then you will teleport! Go north again, but keep going until you reach a route change, where the color will change. Now a wild Pokemon will attack! It will be level 8 (except for Missingno.,). This is how you obtain Mew, Growlithe, and a lot of other Pokemon.
P.S. Whatever you do, do not catch Missingno.!!!
P.P.S. Have fun and test this out, anyone else reading this! (=*,*=)
P.S. BUT WHATEVER YOU DO, DO NOT CATCH MISSINGno.!!!!!!!!!