hey lets post theories better than what was in acually cannon
MY THEORY
takanuva absorbed the rest of light left in the dying jala and put it into his mask and when the thingie symbol floor thing restored all of the light that was lost by using the mask of light and by restoring the lifeforce of jala the ignika noticed takanuvas heroic deeds and restored takanuvas life
Theory 1: It’s a silly kids movie based on a silly kids toy.
Theory 2: You all know how the gold-skinned being had the ability to create anything anyone wished? I think that being a protodermis fusion grants near-Great Being levels of powers, and seeing as how Takutanuva was a protodermis fusion, he had the ability to bring any matoran back to life he wanted to, maybe he even saw that it was Jaller’s destiny to become a Toa, and the future plot convenience force told him “Hey, Jaller needs to be brought back to life, here you can bring him back to life if you want to. Just do it before a few months pass. Oh and you also have only a few seconds to live. Bye!”
Theory 3: It’s a silly kids movie based on a silly kids toy.
Jaller’s revival can easily be explained by Takutanuva’s god-like abilities provided by Makuta. It’s Takanuva’s resurrection that always bugged me.
Because he had to fulfill his destiny, could of been the great beings. Also the makuta can create life. I think that the red star also had something to do with it. Another idea I had when I was young was that if a toa had the power of both light and darkness they could bring back life. But both Jaller and Takanuva had not at that point completed their destinies, which they had to do. In the end its all about their ability to do their duty in order to complete their destiny. Also don’t bring up Matoro because he already fulfilled his destiny so he has no reason to come back.
Makuta created a “shadow Matoran” of him (similar to a shadow Toa), and then Takanuva purified him with light, and the imprint on the mask provided a blueprint for his new soul/AI.