HOLY CRAP! I'm playing through Diamond for the first time ever, and I'm not using cheats or anything else, so I had no idea what to expect...today I went to Mt. Coronet to fight Team Galactic. I made my way up through the mountain without much trouble, but when I got to the top I realized my Pokémon were a little underleveled. I didn't really come close to losing to Jupiter and Mars, but it was tougher than it should have been...I'm still trying to figure out why Purugly is so fast or how it can learn Hypnosis. I hate that Pokémon.
Anyway, I was totally unprepared for three big-time battles in a row. Granted, I got healed after beating Jupiter and Mars, but I didn't expect to have to take on Cyrus and Dialga back-to-back, and I certainly didn't expect Cyrus to get as many hax as he did. His Weavile froze my Lucario two times in a row with Ice Punch, and after I healed him from both, he killed Lucario with a critical hit. I did get what I thought were hax my way when my Empoleon's Ice Beam froze his Crobat, but Crobat was thawed out on the very next turn, so that did absolutely nothing. And then, after beating Cyrus, I moved forward to take on Dialga; I intended to go through a test run without using up any of my healing items, but I didn't realize that the game started the battle automatically once I got close enough--I was gonna do what I have done with almost all legendaries before and save right before battling, but the game didn't even give me a chance to do that. After it killed one of my Pokémon in one shot with Roar of Time, I figured I probably couldn't afford to try to capture it (I wasn't really prepared with a whole lot of Ultra Balls anyway), so I ended up killing it. Ah, well, it's my little brother's game, anyway, so I wouldn't ever really use it.
All that and I was one member down on my team, as I had to have an HM slave for Strength, Rock Smash, and Rock Climb. It was a lvl. 34 Steelix so it wasn't completely useless (it survived 2 or 3 attacks from Cyrus' Weavile and dealt some damage back), but I would have rather have had my full team, of course. If it weren't for Empoleon's numerous resistances I doubt I would have survived that.