Ninja Turtles Adventures #43: A History of the Future.
That's a pretty sweet robot on the cover. The turtles take it down in two panels.
In Part One of the Future Shark Trilogy: The modern-day TMNT, plus Splinter and Ninjara, are recruited by future Don and Raph to help rescue future Mike and Leo. They've been kidnapped by Armaggon, a mutant shark, who has teamed up with classic villain Shredder and new villain Verminator-X. Time travel? Middle-aged Mutant Ninja Turtles? Confused? Don't worry, Don's going to fill us in on the weather.
Future Raph gives Present Raph some advice.
BONUS: Some files from the Teenage Mutant Ninja Turtles Universe Sourcebook!