Short Answer 
In Pokemon Brilliant Diamond, Pokemon stop obeying their trainer at Level 100, where they cannot evolve or battle further. To keep them trainable, trainers should regularly level them up through battles, using items like Exp. Share and Lucky Egg, to ensure they remain engaged and effective.
Step 1: Understanding Pokemon Levels
In Pokemon Brilliant Diamond, each Pokemon has a specific level where they will stop following the commands of their trainer. The maximum level for any Pokemon is Level 100. Once a Pokemon reaches this level, it becomes unable to engage in battles or evolve, effectively stopping its progression.
Step 2: Keeping Your Pokemon Trainable
To ensure that your Pokemon continues to obey you, you must regularly level them up. This can be accomplished through:
- Participating in battles against wild Pokemon and other trainers.
- Utilizing special items like the Exp. Share to distribute experience points more efficiently.
- Using items like the Lucky Egg to increase the experience gained in battles.
Step 3: Importance of Continuous Leveling
Regular leveling is crucial to maintain your Pokemon’s compliance. If you allow them to reach Level 100 without further training, they will be unresponsive and unable to participate in any activities. This emphasizes the need for trainers to consistently invest time and effort in leveling their Pokemon to keep them engaged and effective in battles.