Biollante is a kaiju who first appeared in Toho's 1989 film Godzilla vs. Biollante, and has since appeared in numerous licensed video games and comic books. The creature is portrayed as a genetically engineered clone of Godzilla spliced with the genes of a rose and a human.
Vote which fictional character would naturally fit in-universe with a big-named franchise! No time-travel, no interdimensional crap, no "Pooh's Adventures", they would just exist in-universe.