Mary Elle Fanning as Daisy Jane Allen

James Andrew E. Phelps as Frederick Gideon Weasley
&
Oliver M. John Phelps as George Fabian Weasley

+

sam claflin as barry allen
(I don't know why but after seeing him in Enola Holmes, I can only picture him being an obnoxious businessman; sorry!)

tessa thompson as sofia sloan

chelsea clark as lucy wu

+

and the rest of the h.p. casts as themselves

daniel radcliffe as harry potter
emma watson as hermione granger
rupert grint as ronald weasley
julie walters as molly weasley
mark williams as arthur weasley
bonnie wright as ginny weasley
clémence poésy as fleur delacour
domhnall gleeson as bill weasley
chris rankin as percy weasley
danielle tabor as angelina johnson
etc.