[Clockworkers Doll]

While I totally agree with the idea in general, I agree with Spoops! I would've liked to seen an inside to Remedia's tent as well. Although I'd think it might get the "it's bigger on the inside" treatment. (I had to do that for my RPG maker game too and I've seen it done for almost every RPG maker game, so I'm sure it's not that much of a peeve.)

As for the Arena itself? Maybe a feature to fight a random dungeon boss. Not the Statue of Memories, but just going up to Tarson and saying "I wanna fight a boss!" and then getting put in with a boss and 2-3 normal enemies, just like a Core. But without the Core.
And then I think singles matches need to be heavily improved. Most of my characters can kick arse in there, even if they're not built for PVE or PVP. They're just stupidly easy and it's simple to come up for a strategy for them since they always do the same thing. (only use specials when the Mighty Wall is gone, Cuthroat the mages so they're silenced, etc.)