So basically, because Echo was made with spare parts just lying around the lighthouse, he was sometime clumsy and made mistakes. But he was given feelings like Zane. Anyways, because of this, Dr. Julian would say stuff like “Oh, I never had to clean up messes with Zane,” or “Zane never did this.” Etc. Basically, this made Echo actually hate Zane because he was always compared to him. And when Julian left, leaving Echo behind, he immediately blamed Zane for it.
By the time Jay and Nya came, he had gathered up newspapers about the ninja saving Ninjago (the wind blew them over :))) ) and was so jealous of Zane, he had started to pretend he was actually doing everything and he was part of the team. So he was overjoyed by seeing Jay and Nya, immediately recognizing them. When Jay recruited him, it was basically his dream come true. However, when he met Zane, he was disappointed and felt betrayed because the team he was on was just temporary. Then Jay made his wish, blah blah, everyone forgot except Jay and Nya. And Echo.
So basically, Julian was a very famous inventor back in the day and he had tried making a time travel machine thingy. But it didn’t work. All it did was prevent time travel actually. The hands moved slower or faster than it was supposed to sometimes. This meant that if the clock was taken forward or backwards in time, it would still show the same time as before, remain the same, etc. He later used it when making Echo, so, therefor, when everyone else forgot Skybound, he remembered.
Echo was sad about this and wanted to see Jay and Nya again since they were his only friends. Then, every once in a while, Jay would come visit, feeling bad. Jay was surprised he remembered but didn’t question it. Echo always asked why he didn’t bring him back with him and was always answered with the same thing.
So, after a while, Echo started to blame himself. Then one day, a girl came to visit the lighthouse, hearing about how a great inventor used to live there. Wanting to maybe recruit him, she instead found Echo.