You are going to have to either use a cheat or catch it with a Master ball.
level him up to level 30
It evolves at a level 30
It elevates your Pokemon up one level.
you can get arceus at level 80 in platinum by getting a 100 win streak in the battle tower.
There is no trainer with it, but you can evolve remoraid at level 25.
Luxio evolves into Luxray exactly at level 30 on Pokemon platinum.
Then you have a level 70 pokemon!
Giratina is level 47 in Platinum and level 70 in Diamond and Pearl
level 30
Level 100
at level 34
Arceus
Level 934, that's the highest they go.
At level 10.
level 44
level 26
level 26