The Mostly Invisible Boy (Casey Grimes 1)

This "wildly imaginative" (Book Pipeline) "splendid conception" (Kirkus) from upstart author AJ Vanderhorst celebrates the transformative power of courage, tenacity and a little skill with a battle-axe. Set in an alternate USA where monsters prowl, this debut novel is told from the perspective of mostly-invisible-but-still-hopeful Casey Grimes.
Eleven-year-old Casey is stubbornly friendly, but he's eternally the new kid at Vintage Woods Middle School. Students look right through him—and they're not faking. Casey doesn't know why he's mostly-invisible, but when he scales a colossal oak, he discovers a fortress in its branches. The forgotten sentry tree marks the border between his safe, suburban life and a fierce frontier.
Casey and his little sister Gloria infiltrate Sylvan Woods, a secret forest society devoted to ancient, wild things. Sky-high footpaths. Survival sewing. Monster control. Shockingly, people here actually see Casey—but being seen isn't enough. He wants to belong.
Keeping his identity hidden--while struggling to prove he fits--is hard enough, but Butcher Beasts have returned to Sylvan Woods after a hundred years. Trickery is under siege. As the monsters close in, and the fearsome Sylvan Watch hunts Casey down, he and his newfound friends must unearth abandoned magic, buried at the forest's roots...or be devoured along with everyone else, Sylvans and civilians alike.
A fast-paced middle grade fantasy/adventure book with all the monsters kids could ever hope for.