Ok here's the revised version of my old idea. It would be a shop called "Sasuke's Gym" and would be located in the special village. By being located in the special village only sannins and up could use it.
Sasuke's Gym.
You walk into Sasukes Gym and see an assortment of weights, dumbbells, and a large track. You see Sasuke sitting on a counter surronded by a group of cute girls. You walk over to him, but he doesn't seem to notice you. Finally he glances at you saying, "What do you want punk?" From here you could either walk out of the gym telling yourself your strong enough already or, you could train with Sasuke.
A1. Strength Training: You tell Sasuke that you have come to work on your strength. He smirks and says, "Yea you look like you could use it buddy." After a few hours you emerge from the gym feeling stronger than ever! You gain 1 temporary attack point which would vanish after a DK. Maybe that Sasuke kid actually knew what he was doing in there! The cost would be 1500 Gold and 3 Gems.
A2. Endurance Training: You tell Sasuke that you have come to work on your endurance. He laughs and says, "Oh well if you insist I guess I can help you." After a few hours you emerge from the gym feeling more energetic than ever! You gain 1 temporary defense point which would vanish after a DK. Maybe that Sasuke kid isn't as arrogant as he seems. The cost would be 1500 Gold and 3 Gems.
NOTE: THE GYM COULD ONLY BE USED TWICE PER DK. This would prevent anyone from having massively high attack/defense.
Plus this being located in the special village would mean it's only available for upperranking players.