I have competed the entire game at least 3 times and there is no possible way to re-battle any of the gym leaders
You can't unless you restart the game.
Rival
No, you don't. You cannot face the Sinnoh Gym Leaders in HeartGold.
Of course you can. I played my Pokemon Diamond with my cousin that has Pearl.
On the marking map you can't mark Pokemon but if a Pokemon is roaming it will be represented by a Pokemon face.
I don't think so.
face it and press A
the god of all Pokemon in diamond is........ (enter dramatic music here) ARCEAS!!!!!!!! (luckily it's not ur face!!!!!!!!!!!!)
Scary Face is not a TM or HM in the game. It's a move that Pokemon can learn by level up or by breeding.
you need an action replay when you get there you will face shaymin at flower paradise
Face the Pokemon League again
You can't