Board Thread:Questions and Answers/@comment-25512318-20180406161723/@comment-34175192-20180510213856

Some villains are more likely to return than others.

The Overlord is presumably destroyed. Morro is dead (rip buddy) so they are not likely to return.

However, Pythor always shows up, Nadakahn is still trapped and the Time Twins are lost in time. If Wu can get out of the vortex, they can too.

Hang on. Garmadon was dead. He came back...

Well that just ruins my whole explanation.