Since last year I'm trying to enter the castle the first time I took a dc and I couldn't get in again I asked what was the problem and if I could reset my quest, now I need it because I want the gengar mega stone and need it, they could help ?

You have to respawn Alucard in his Castle on the third floor, by defeating the Horon boss in the Dark Valley (north of Necropolis).
Make sure to not let any pokemon of you faint while battling Horon. If you didnt get the Rapidash Mount from Horon yet, you will get rewarded with the mount on beating Horon. You have to wait 3 days for Horon to respawn after that. If you beat him again, Alucard will respawn and you can enter his castle again.
Defeat Alucard with a pokemon that has the move Miracle Eye on your party and you will find yourself on Dark Realm again.

 

Edited October 12, 20205 yr by Norex