you don't but you can put in fire red, leaf green, ruby, sapphire, and emerald and go in the red eyed room in the old chateau.
yes
152 is rotom.
An event
you can't
You can't, you have to Migrate him over or trade.
You can't catch Mewtwo in-game in Pokemon Diamond.
To get a Gengar, you must trade a Haunter and it will then evolve into a Gengar.
It is impossable to get one in Pokemon diamond,but there might be one in Pokemon platinom...... hope that helped!
you cant find gengar if you not have steal trainers Pokemon cheat
gengar can defeat any Pokemon same with any other Pokemon
Gengar is a Ghost-Poison type.
Golbat uses mean look in Pokemon pearl but i am not sure about Pokemon diamond and pearl.