My mystery figure is rectangle.
I purchased this Harry Potter Collectors Keyring Series 1 mystery bag for about $6.
I purchased that particular bag because it either contains a Hogwarts Train Ticket, or The Monster Book of Monsters (Exclusive A). I'm looking for both of those key rings.
The quality is a lot better than I had expected. The rectangle part of the key chain approximately 6.25 x 3.5 cm.
This is a corrected copy of that key ring. "Platform" was misspelled "Platfrom" in previously manufactured copies.