Killing a major character in basically the first episode was, highly unusual.

And forcing the other X-Men to deal with that loss in subsequent episodes, isn't something you see in children's TV EVER.

Even when they finally brought back Morph (This is a comic book show, no one can die forever), he wasn't really the same. Everything didn't go back to being ok, he was permanently damaged and had PTSD from the experience and was unable to join the X-Men.

As a 6 year old who had family members with PTSD, this cartoon connected with me like nothing else would until I was a teenager and able to read real literature.