I've played the Battle Frontier both alone and online play, but I've never played it locally.
Mostly, I'm interested in playing with my girlfriend, who has Diamond, while I have SoulSilver. Are we able to do the battle tower with each other? Also, there's like an arcade battle room in the Battle Frontier in SoulSilver with a game board - does that exist in Diamond?
Where do we go to run through Battle Tower? Is there anything we can't do together because it's not in Diamond?
(Sorry if the question is worded poorly, I haven't played DPPt and am not sure what features it does or doesn't have compared to HGSS)