Jinx are a race of hermit crab like creatures that live on land, and wear stones instead of a shell (as per KQ5). Graham is said to have kept jinxes as pets when he was young. So they apparently make good pets. They are likely natives of the Serenia woods between Eldritch (KQGS) and Serenia (KQGS), and also near Llewdor (KQGS) where Graham was said to have lived.