I need help on pokemon diamond version

Question

can someone tell me where cynthia is and how to get the secret potion from her

Answer 1

After beating the 5th gym leader, Cynthia will show up and give you the Secret Potion. Or maybe it was the 4th gym leader. If it is, talk to a Galactic grunt right next to the Safari Zone. Chase him down and then battle him.

Answer 2

did you beat the team galactic grunt that you have to chase around? after  you do you need to go further a little then cynthia will show up

Answer 3

Cynthia will be waiting for you after you win the Relic badge at hearthome city gym.  You can go there after you talk to Cynthia's grandmother and get surf.

Answer 4

This should do it

go to the valour lake front and go south to the beach an then if you go north you should get to a hotel (if not go to the beach an keep goin right) and use your poketech app (the radar thingy)to look for the womans suite key give it to her an she gives u a lava cookie then go to the safari park in pastoria city dont actually go in but heal your pokemon then talk to the galactic member just to the right of it u should hear him speaking then he will run off follow him then you will fight your friend (whatever you named him), as long as youve got 25+ levelled pokemon an a good mix (e.g. a water a fire a grass... etc.) i beat him with around level 25 geodude ponyta staravia chingling machop and my prinplup then once youve beaten him follow the grunt again he runs off to the lake stoppping every so often to think ...aloud... and then you speak to him and he will run off again do that about 3-5 times an finally will battle you just at the lake u should beat him then he hobbles off and you see cynthia standing infront of those 2 people in black guarding the lake speak to her and she will give you the superpotion!