Also, before I thought Mr. Grim was Peter Pettigrew, but now that we know that Black is the actual bad guy, it’s even clearer that Mr. Grim = Sirius Black.
Mr. Grim is also a reference to canon, because The Grim is an omen Harry sees which turns out to be Sirius in his black dog animagus form.
Mr. Grim is also a reference to canon, because The Grim is an omen Harry sees which turns out to be Sirius in his black dog animagus form.