The imaginary / Harrold, A. F.

Rudger, an imaginary playmate, must find his friend Amanda before he fades away to nothing, while eluding the only other person who can see him, evil Mr. Bunting, who hunts--and possibly even eats--imaginaries.

No friend is perfect--Rudger, Amanda's Shuffleup's friend, is imaginary. That's his imperfection. Even so, Amanda has fun with Rudger--but then the sinister Mr. Bunting arrives at Amanda's doorstep, and he hunts imaginaries. To save Rudger, Amanda has to stop imagining him--but that might be his end as well.