Sorry to say, but Gengar is not obtainable in the wild.
you trade him. and he will evolve into gengar. you trade him. and he will evolve into gengar.
Piplup is obtained as a starter in Diamond and Pearl or through trades.
Get a Haunter and trade it with a friend in the Union Room, then it will evolve into Gengar if it doesn't have an everstone.
trade it from soulsilver
A good team for Pokemon diamond or pearl is probably Empoleon, Staraptor, Roserade or, Steelix, Machamp, and Haunter or Gengar.
Sorry, but Entei can not be obtained in Pokemon Diamond and Pearl itself, you must transfer it from old GBA games and use the Pal park in DP to catch him.
Put Honey on a tree
You have to migrate from Sapphire or Emrald.
Misdreavus cannot be obtained on Pokemon Diamond, so you must trade one from Pokemon Pearl.
The TM is roost but I don't know where to find it
look near rocks or evolve geodude
Transfer from Platinum, Pearl, or Diamond It was obtained from TRU event