I've had multiple people comment on my submission complaining that there are no ghosts, even though the theme is not technically required.
I feel that this is a common and recurring problem with minijam that hurts a developers chances of winning, and leads to a less cohesive body of submissions. In future jams, I would suggest waiting to announce the theme until the jam starts, making it required, and getting rid of the required "limitation" altogether, which tends to be overly constraining and unrelated to the theme.