For some time I have had in mind a one-shot volume on Dragon ball that I read years ago, almost certainly unofficial since I searched for months without results. I remember a little about the plot, not much: I recall that it centered on a tournament in which Goku and Gohan definitely participated, probably Vegeta and Trunks as well. The tournament final was reached by the fighters getting on “shuttles” that moved in long tubes. More of the plot I don’t remember. I know I bought it around the 2000s.