This is soo hard!! For me it's HeartGold and Platinum. HeartGold was so cool, I just loved almost everything about it and also that you could visit the Kanto region, that was so cool. It would be so fantastic if you could visit in every game the other regions. Platinum was just epic for me. Oh and for both games, that it could be day and night!!! It was sooo cool!!
My favorite new pokemon from Platinum must be Acreus. The God Pokemon. It is actually the God, he created Earth. It was so epic to play that flute and then all of the sudden a magic stair appeared. It was magical.
The easiest Gym in Heart Gold was ''Rock'' when you defeated the Elite Four, you could travel to the Kanto region. He was so easy because my starter pokemon was Chikorita. The hardest must be the last gym. In Platinum it was the Pastoria Gym, the water gym. I had Turtle as a starter, that grass pokemon, the ghost gym was so hard!!
My favorite place in HeartGold was where Lugia was. It was so beautiful and it looked so epic. And it was so epic!! In Platinum is it the Distortion World where Giratina was. Later it was pretty boring but when I first came there it was soo cool!!
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The game was just so awesome. I appreciate that there were 16 gym battles and so much to accomplish. And I remember playing it for the first time and being so excited that it incorporated day/night and weekday systems. 
Emerald had the Battle Frontier. 
