Unused Platinum Rival Battle
There exists a set of unused rival battles in Pokémon Platinum. No script in the game calls these battles, so they are completely inaccessible through normal means. Barry's highest level Pokémon is his starter at Level 75, falling between the base Survival Area weekend battle (Level 65) and the one that unlocks after twenty Hall of Fame entries (Level 85).
The Trainer IDs for these battles are 840, 841, and 842, the same IDs used in Diamond and Pearl for the upgraded Barry battle. However, the movesets and levels are slightly different from their Diamond and Pearl counterparts.
While there was previous speculation from the community that this battle was supposed to unlock at ten Hall of Fame entries, there is no evidence whatsoever that this was the original intention for these unused battles.