you just have to keep leveling up your pokemon. Try different areas that fit your pokemon's level. Hoped this helped!!
the highest level in both diamond and pearl is level 100
At level 100
no you cant
No, you cannot.
Train your pokemon.
The highest a pokemon could be is level 100.
level 100
There exists no trick to get a Level 100 Regigigas in Pokemon Diamond, except by manually levelling up the one found in Snowpoint Temple.
beat him with a level 100
any level up to 100
in diamond--level 30 pearl--level 30 emearald--by trade or by level 100
ergfergfs