The endgame boss rush of Final Fantasy 6 is probably the most creative final boss in the entire series, and it gets complicated before you even start fighting. You come in with up to twelve characters, and have to arrange them in order - the fight goes in four stages, and any character that's knocked out at the end of the stage gets replaced with the next character in the list for the next stage. And every stage loves to blow the crap out of at least one character when dying. It gets even better, because only gives you enough top-tier equipment to make about six characters invulnerable (the most useful six, at least), but the dungeon right before it all but encourages swapping equipment around between the three groups that you bring characters in.
And of course, the game doesn't tell you any of this, so if you just walk right into the big cutscene, you're likely to face the final boss with a slapdash party with no equipment. At least there's a save point right before the end.
Why Happy you ask? Because this game is awesome, and the ending is awesome and requires some strategy. Every dungeon before the end gets pretty trivial by the time you finish them. The final dungeon is a noticeable step up in threat when you get to it, but you master it fairly quickly. The "mini"bosses before the end should be serious challenges, but gimmicky party builds and nukespam can stomp the crap out of all of them (it's almost trivially easy to beat the mighty Guardian in seven hits). But Kefka's tower of power is good enough to nullify even those tricks if you're not careful. It's a worth end to a worthy game and I love seeing it.