SOLVED. Children's Fantasy with Monster and Witches; Main Character shows signs of OCD

[K]

I’ve been trying to find this book for months and for months it has eluded me. I read it about 8-10 years ago in the US. It was a childrens/middle grade book with fantasy elements. I don’t remember the plot too clearly but I do know that there were two main protagonists, a boy and a girl. I believe they were school friends but they could have been brother and sister. I distinctly remember that the boy had some sort of OCD quirk where he had to knock on the walls a certain number of times to make his bad feelings go away. This originated from his fathers death/disappearance I believe. In the beginning the boy and girl go out to investigate something in a graveyard and have to hide in a mausoleum. There they discover this big monster, who may or may not have been purple (my mind might have made that up). They are at first wary of this monster but eventually partner together with him to save the world from some evil witches who want to enter through some portal. I just remember there were a lot of scenes in tunnels and traveling through tunnel/slide like portals. I don’t remember much else other than that, though the cover might have been of the purple monster. Again not super sure. Thanks in advancedddd!

[K]

SOLVED it's always October by Bruce Coville

[SamSpayedPI]

Always October by Bruce Coville for the link.