even Exodia's severed limbs are equal to a decent normal monster, so together he's supposed to be unstoppable.
... his severed limbs are actually very weak in a fight. 200 attack compared to a somewhat standard(for a level four monster) 1800 or 1700. There's a reason you have to keep them in your hand.
If you don't want to bother with Exodia, there's always Jackpot 7...
Destiny Board(which in Japanese version spells DEATH, US version is FINAL), Final Countdown, Last Turn, and a few others I don't recall. There's quite a few instant-win setups in Yugioh. Exodia is actually one of the weakest unless you have a setup to draw every single card in your deck in a single turn(and those
do exist), since those limbs take up space in your hand(limited to six at the end of your turn. I know of at least two cards that increase that). Not only are the limbs weak, the main body is too.
Destiny Board is hard to pull off since Mystic Space Typhoon is something every deck should have at least two of, plus many other cards that can take down your Magic/Spell cards, but it will win you the game in five turns if they
don't manage to kill you or any of the letters. Final Countdown needs to be played early, then you need to stall for 20 turns(10 of yours, 10 of theirs). Last Turn is dependent on having a single really powerful monster still undrawn in your deck and your opponent having a weaker one in theirs. It's a bit finicky, since any effects that create a situation other than where only one of the two monsters is left alone on the field results in a draw.