The Not-So-Perfect Planet Way-Too-Real Aliens Series, Book 2.

Josh Higgins has an alien gizmo that lets him think his way to other planets-and he does NOT want to use it. But his sister Maggie won't stop bugging him, so he agrees to an off-world vacation. Josh dreams up a planet full of blue oceans, white beaches, and sunny weather. And he prepares for everything...well, almost. A parade of cranky creatures soon spoils Josh and Maggie's perfect getaway-including a one-horned beast, a sharp-toothed sea princ...