How do you catch typhlosion in Pokemon Diamond?

You can't catch Typhlosion directly in Pokemon Diamond. Typhlosion is the evolved form of Quilava, which is the evolved form of Cyndaquil. To get Typhlosion, you need to follow these steps:

1. Choose Cyndaquil as your starter Pokemon. This is the only way to get a Cyndaquil in Pokemon Diamond.

2. Level up Cyndaquil to level 14. At this level, it will evolve into Quilava.

3. Level up Quilava to level 36. At this level, it will evolve into Typhlosion.

There are no wild Typhlosion in Pokemon Diamond, so this is the only way to obtain one.