Load the game, and select the 'Moon' level in free play.
Make sure you're in 'build mode' rather than 'drive mode' (press
if needed), then press left on the D-Pad
to switch into alternate building mode, which means items can be placed in mid-air.
to open the spawn menu, and find a bicycle-with-basket under 'vehicles'.
Press up on the D-Pad
to rise up (best to do this a few times), and place the bicycle in mid-air.
again, and find an alien passenger under 'sci-fi' (bottom row) on the far right. Hover directly over the basket, and place the passenger in the basket.EDIT: If it doesn't pop, AlbinoKidELITE suggests placing the bike high up in the air, and YodaFreak1984 suggests making the alien face the same way as the bike. You can rotate pieces with .