Amos and the Alien — Gary Paulsen

When Amos and his best friend Dunc have a close encounter with an extraterrestrial named “Girrk,” Dunc thinks they should report their findings to NASA. But Amos has other plans. Not only does he promise to help Girrk find a way back to his plant, he invites him to hide under his bed! Then weird things start to happen -- Scruff can't move, Amos scores a game-winning touchdown, and Dunc knows Girrk is behind Amos's new powers.
 
What's the mysterious alien really up to!?