No, Mew is a real Pokémon so it won't harm your game.
trade from a different game
Yes it can but you will need to have beaten the game
Yes, Pokemon Red can trade with Red, Blue, Yellow, Gold, Silver and Crystal.
No, since Pokémon Yellow is on the Game Boy Color, and Pokémon Fire Red is on the Game Boy Advance, it is not possible to trade between these games. The Game Boy Color is not compatible with the Game Boy Advance.
gold, red, blue, yellow
Because it can't
nowhere. you need to trade it from a different game
No you cannot trade from Game Boy Color And Game boy Advance.
You'll need to trade in 9,999 coins in the Game Corner for Porygon.
You can't. The only way to get Raichu in Pokemon yellow is to trade your Pikachu to another game, give it a thunderstone, and then trade it back. I don't suggest this however, as once it is evolved into Raichu it will no longer follow you around in-game. Your best bet - if you want to take the time - is to catch a new pikachu (not available in yellow) on another game and use the thunderstone there and then trade it.
Sorry but it would be impossible because for one thing Leafgreen doesn't exist the same time pokemon yellow did so they would be too many years apart and a gameboy color game can't trade with an advance game what you need to do is own one copy of each game and trade to an advanced copy that you can trade with like if you can trade yellow with gold for example. then eventually you could trade to leaf green..if that works. You can always just trade between Leaf Green and Fire Red...whatever pokemon you wanted to trade should be in either version anyway.
Yes you can but you have to use a connectre cable to do that.