My gaming mystery isn't any one thing
per se (if I had to choose one, it'd probably be
pra-mai HellValleySkyTrees), but I'd really be interested to know more about the scrapped enemies from the first two Paper Mario games. Only recently did I ever see what became of a few of the scrapped enemies from
Paper Mario 64, but there's a good deal of PM:TTYD enemies we know little about.
Curiously though, when poring through enemy item drop tables in PM:TTYD whilst making
this guide, I stumbled upon a couple of interesting anomalies in the Glitzville enemies' drops. The Dull Bones set all have Bob-ombs' normal drop table, which might suggest that they replaced the missing
Hyper / Ultra Bob-omb. More strangely, the Lakitu and Spinies set have the item drops of Ruff, Ice, and Poison Puff, suggesting you might have fought a group of various Puffs at some point. Fun stuff!
Also, I suppose this makes as good as a Halloween avatar as any.