Pedegree455,415 Locked 14 Dec 2011 11 Aug 2012
This is easy.
In the main menu go left till "Sandbox" to enter it, then choose a Saveslot. Then you go to "Edit Level", press Start and go to "save + play". Now you can drive, while pressing for and back on the Analogstick for an "Wheelie" and an "Endo". So you can get a X100 Combo. After you had it, the combo is "registred".
The "Mega Combo!" Achievement DON´T pop up yet.
Leave the Game, go to the Editormenue and choose "upload level". Send one of your Buddys a message, with your Level and it will pops up.Your Buddy don´t need the game for this! So you can get the "SHARE THE FUN!" Achievement at the same time. So it´s worked for me.
Maybe this way is the fastest & easiest.
NOTE:
I have edited the solution a little bit.
Thanks to onnovdw, KP ScuzzyBunny & AGKuma for their tipps.
NOTE2:
For the negativ voters:
Please subscribe, what´s wrong or unclear for you!!!!
I made a Video for this: