Like the title suggests, what's the hardest dungeon and antagonist you faced in PMD, as in like fighting Dialga in Temporal Tower and Rayquaza in Sky Tower, or Kyurem in the new 3DS Mystery Dungeon game. Because everyone at least struggled to beat that obstacle(s) in PMD.
For me, Dialga was extremely hard. I faced Temporal Tower and had no problem with each Pokemon except Dialga. Its Roar of Time was hard to escape except if you use Smokescreen, Detect, or Protect and have a lot of Reviver Seeds and Oran Berries. It took like a long while to beat that.
But in Sky Tower, Rayquaza was no trouble, but on the way to battling him, Aerodactyl kept annoying me with its unbelievable damage, I mean, its Bite attack can take 60% of a Pokemon's HP or Wing Attack which can almost kill a Pokemon. Because of that, I had to redo that dungeon at least twenty times.