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Eternal Forms for all pokemon that aren't fully evolved.
Eternal pokemon have increased stats that are comparable to its final evolution. Stat wise it can work two ways.
1- Each eternal form gets the same base stat total as its final evolution but distributed in different way(eternal rhyhorn is faster than rhyperior)
2- Each eternal form has the same base stats as its final evolution
Design wise it can work two ways
1- Each pokemon keeps its original design but gets eternal flower colouring.
2- Each pokemon stays exactly same.
In addition eternal pokemon get a intro animation like shinies and have a symbol next to their name like mega pokemon. Also pokemon that have been changed to their eternal form are considered fully evolved by the game so evolite and evolution items no longer work on them.