Dwayne Johnson Dr. Xander 'Smolder' Bravestone Kevin Hart Franklin 'Mouse' Finbar Jack Black Professor Sheldon 'Shelly' Oberon Karen Gillan Ruby Roundhouse Rhys Darby Nigel Billingsley Bobby Cannavale Van Pelt Nick Jonas Jefferson 'Seaplane' McDonough Alex Wolff Spencer Gilpin Ser'Darius Blain Anthony 'Fridge' Johnson Madison Iseman Bethany Walker Morgan Turner Martha Kaply Mason Guccione Gamer Marin Hinkle Spencer's Mom Tracey Bonner Fridge's Mom Maribeth Monroe Teacher Missi Pyle Coach Webb Marc Evan Jackson Principal Bentley Carlease Burke Miss Mathers Colin Hanks Alex Vreeke Jason New Bivouac Biker Rohan Chand Kid at Bazaar William Tokarsky Bread Vendor Tait Fletcher Scorpion Recipient Stephen Dunlevy Transportation Shed Guard Rob Mars Transportation Shed Guard Virginia Newcomb Alex's Wife (uncredited) Maddie Nichols Kid #2 (uncredited)