Some TMNT stuff really isn't for little kids.
Donatello from an alternate future, he gained incredible wealth selling his inventions. He is depicted as a pure-hearted soul, being able to pass through the Netherworld unscathed. Don was also chosen by a group of alien scientists known as the Sons of Silence to share their wisdom to him.
In the future Donatello had gained incredible wealth selling his inventions to benefit mankind, one the actions of his inventions according to Armaggon had wiped out the rat problem and population. He also had a kind assistant and protégé in the form of Manx a mutant anthropomorphic cat had altered his body with Cybernetic implants that drove him insane and became the villain Verminator-X. Donatello had also created both battle suits for himself and his brothers. Along with a time machine called the "Time Slip Generator".
Future Shark Trilogy
Armaggon, the evil mutant shark, traveled to past where he teamed up with both the Shredder and his former student Verminator-X. Using his time machine, Donatello and future Raphael traveled to the past to warn their past selves and also seek out their assistance in saving future Leonardo and Michaelangelo, who had been captured by the Shredder, Verminator-X, and Armaggon. The turtles chose to help their future doppelgängers and went to the future where they were shocked to learn not only did they live in the public, but were incredibly wealthy as well thanks to Donatello's numerous inventions, mostly his re-design of Baxter Stockman's Mouser robot. The six turtles and Ninjara fought the trio of villains with their unexpected ally the Rat King and freed the future versions of Leo and Mike, along with Merdude who had been captured by Armaggon unbeknownst to any involved.
Future Donatello and Raphael were later seen helping the Mutanimals build their new base of operations, but between returning to the future and coming back to the past, the Mutanimals were killed by the Gang of Four. Upon hearing gunfire, Slash, who had also been on the island at the time, assumed that the future turtles killed the Mutanimals and a battle ensued between the three turtles. After the future turtles cleared things up with Slash, the three sought the help of the present-day turtles, and confronted Null, Maligna and their thugs. In the aftermath Slash lost his life, an event future Donatello said never should have happened, and that in their timeline Slash was still alive and the Mutanimals had been killed by Maligna instead of the Gang of Four. It was then that the future Donatello realized that the Time Slip Generator had not taken him back to his past, but the past of a completely different reality, one he had no business interfering in.