The way u can get gengar is to evole gastly all the way to haunter than trade it wih someone than u get gengar
That is Gen. 4
no, you can not because its a 3rd gen to a 4th gen only the same gens can fight
You cannot get Zekrom in Pokemon Platinum because Zekrom is a gen V pokemon and pokemon platinum is a gen IV game. Since Zekrom did not exist inside any pokemon game at the time of platinums release It's impossible for him to be inside the game at all.
No, it does not have a new evolvloution in this gen.
No. They are completely different games (/black are V gen whereas platinum is IV gen). However, Pokemon platinum does share many similarities with Pokemon diamond and peal.
None - Pal Park from 3rd Gen.
Ekans is one of the missing Pokemon in platinum. You can catch him by importing him into the Pal Park through a Gen II or III game.
Kyogre is in Pokemon games emerald gen.3, ruby gen.3, sapphire gen.3, firered gen.3, leafgreen gen.3, diamond and pearl gen.4, platinum gen.4, heartgold gen.4, soulsilver gen.4, black gen.5, wight gen.5, black 2 gen.5, wight 2 gen.5,
shaymin sky forme is only available in platinum and gen. 5
The only region in Pokemon Platinum is Sinnoh (Gen. IV). You can also travel to Reverse World, however it is not considered a region.
You can't because regigigas is a 4th gen pokemon. If you want a regigigas then you will have to migrate Regice, registeel and regirock to Diamond, Platinum or pearl
You have to trade it over from a 4th gen game (Diamond/Pearl/Platinum) or from a friend. You can't get a Prinplup otherwise.