Dexter's Laboratory: Ego Trip.

After Dexter is confronted with robots who wish to "destroy the one who saved the future," he uses his time machine to see how he saved it. They declare that they are here to destroy the one who saved the future, and make ready to attack Dexter. Dexter easily destroys them with the use of various tools and gadgets from his lab. However, news that he is "The One Who Saved the Future" intrigues him, and he decides to travel through time to discover how cool he is. In the first time period he visits, Dexter finds a tall, skinny, weak version of himself working in office-designing cubicles, with Mandark as his rich, successful boss. The child Dexter unwittingly reveals the existence of blueprints regarding the "Neurotomic Protocore", and Mandark steals it after the two Dexters move forward in time.