Well, maybe exspecto patronum.
Yeah, I expect I didn't notice that because of "expect", but it seems to be expecto in print so it's actually "I comb out a protector."
Patronus is in the accusative case
You're right, I jumped the gun on that.
But the -r- doesn't make much sense.
The spell is "Disarm" so the r is supposedly from arma. If you ignore the "r from arma" connection, expellere, expuli, expulsus should have no 3rd conjugation verb ending with an -iamus (and why one spell with 1st person plural "we"?). If it's not a verb, the nouns based on that verb should be from the supine expulsus, e.g. expulsio (a driving out, expulsion), expulsor/expultrix (one who drives out), etc.
Most of the spells are "I do whatever" but the spell that stops another spell is "(imperative you
plural) end the spell!" (finite encantatem). If I can do most things myself, why do I need this mysterious other "y'all" sometimes (or even "we")?
Don't get me started on the school-year-long quidditch season that consists of only three evenly spaced games.