[sarcasm]Yeah, those bosses are a real joke there! Why, you just have to level up infinitely and have combos of multiple copies of the game's rarest or unique items! W3@k d00d![/sarcasm]
The FF7 weapons are hard, but not impossible. Emerald deals damage based on your materia, so just don't have much materia equipped for him. Ruby, go in with two party members down, as noted. But I beat both of them without KotR, many tens of levels below 99. I make a special point of NOT using KotR, as it is the cheapest spell ever created for any game (except maybe Barrier in Secret of Evermore), as it just sucks all the challenge out of the game. Just because it's there doesn't mean you have to use it!
As for Omega, well, there's two main ways. The first way is technically cheating - force the game to halt on Selphie's limit break (by opening the CD tray/cover as a spell animation starts for another character) and then force her to get "The End" as her limit (only works if she's Aura'd and injured). The second is to have a party of Squall, Zell, and Rinoa, all whacked down to critical injury mode before you engage Omega. Have Rinoa use her limit, and it will almost certainly be Invincible Moon and last longer than you need to finish the battle. Then just do Squall's limit (preferably lionheart) over and over and Zell's ultimate god combo over and over (booya + punch rush, rinse repeat). Again, possible many tens of levels below level 100. (Just don't be a multiple of level 5.)
Ozma, well, Ozma is overrated too. The main key is to have your party include Zidane and Freya who will automatically do 9999 damage no matter what, even if Mini and status-screwed, and you can accomplish this feat many tens of levels below 99. The key is to steal through the whole game with Zidane every chance you get, since Thievery deals non-elemental damage based on your steals; and kill a bunch of dragons, to build up Freya's Dragon's Crest. (As a bonus, the grand dragons on the plateau by Gizamaluke's Grotto out the side exit give tons of XP to build you up while you're doing this, and they can be instantly slain with level 5 death.) Then just have your two white mages in the party to heal constantly.
But anyway, I think the hardest game ever made is probably Out of this World. Do everything exactly right all the way through the game or die, yey! And the ending's not even worth it, although the game itself is pretty cool for all its funkyness and insane difficulty. Every extended fight is like a boss battle, setting up your force shields is very important, etc.
A little more on topic to true bosses... probably the hardest boss fights for me are "mini-game bosses." I'm just not good at some of these minigames which have no relevance to the game in which they reside, so encounters like Topo's Groove Heaven (in Brave Fencer Musashi) or Mz Ruby (in Sly Cooper) really cheese me off. At least with Mz Ruby, you chould "cheap it" by pausing and unpausing a lot. Probably the single hardest freaking minigame boss of all time is that speeder race in the palace in Starfox Adventures... jumping Jesus on a pogo stick! It took me forever to clear that! Definitely the hardest boss battle ever, from my point of view...
