Donatello (sort of) killed the Shredder the FIRST time. That was really a group effort though, as Donatello certainly didn't wear him down himself.
DON: This is the end for you, Shred-- OOF!
SHREDDER: You are overconfident, fool!
...Yeah. In the end, though, Don knocked him off the building and his thermite grenade exploded in his hand before he could use it for anything damaging to our heroes.
However, by using a blend of ancient Japanese magic and science, the Foot clan was able to resurrect their master. They found all of the Shredder's pieces, had worms eat them, did some tests, cloned the DNA, and ended up with four Shredders- well, one real Shredder, and three freaks, made from the worms that were dressed like Shredder. The turtles confronted these guys, but just as the fight got underway, Raph said, "Saki is mine!" Leo said he couldn't, they have to stay together, and chased him, leaving Mike and Don to deal with midget Shredder, lobster-claw Shredder and humongo four-armed Shredder (who were all good fighters, despite their looks... and they were later joined by more Foot members, including Shredder elite guards and other good fighters) Leo found Raph just about to be killed by a Shredder elite guard. He reprimanded Raph about how they were taught to stay together and told him to go help his brothers. Meanwhile, Leo took on the Shredder...
The fight was great. If you wanna see it for yourself, hunt down Mirage #21. It ends with a huge explosion. The turtles think Leo is dead, but then, he comes in with a bodybag and proclaims: "Oroku Saki... The Shredder... is dead. It's finished. Our destiny is complete. We have... one final task..." So they burned the body and stuck the mask on a flagpole, and lived happily ever after... except for the Foot's constant attacks, but that story can wait for another time.
