Version 1.1 (roughly 8GB)
- multiplayer functionality
- additional game fixes
- audio for supported languages other than English
So the multiplayer download IS required if you want bug fixes, as I suspected.
It's required if you want to play at all...
This definitely got my goat when I saw the patch and the requirement.
Literally no reason to buy physical games if all you need is a titanic assortment of SD cards.
I hadn't updated the game and had no problem other than a crash after my first death. After that it was smooth sailing. Lucky for me I intended to update for the multiplayer mode anyway, which I'm doing right now.