Many ways:
footprint ribbon, lady in Pokemon fan club (hearthome city), or the poketch app that lets you grab the Pokemon in your party (hearts will appear if it likes), or the man in celestc town Pokemon center (he will give you a great ball if your Pokemon likes you).
Southeast of Pastoria, Doctor footstep will give you a few sentences about how your Pokemon feels about you. If your Pokemon really likes you he will give you the footprint ribbon.
there are none that i know of in diamond. sorry(-_-)
as far as I know you can't get entea in pokemon diamond unless you trade.
There isn't a flute maker in Pokemon diamond as far as I know.
It depends... What Pokemon is it? (Not that I know...)
YES!they are only friend but i know that they will be couplesNo, Dawn may like Ash, but Ash likes Misty!
well i do not know
The Legendary Pokemon in Diamond are Dialga, Azelf, Mesprit, and Uxie. That's all I know of.
You cant get a piplup mask on Pokemon Diamond or Pearl u can get it but i don't know how
Will you tell me what is that pokemon?I don't know what is the 47th pokemon....
Uh, yeah. I don't know who this 'Hubert' is, but who cares whether he likes Pokemon or not?!
To get a Venusaur on Pokemon Diamond you have to get the National Pokedex and look for its area, if it's unknown then I don't know what to do.