Water/Bug
I don't see how we'll make a Defensive Pokemon that differentiates itself from the dominant defensive/bulky waters past and present of the meta (Arghonaut, Toxapex, Alomoloa, Milotic, Suicune, Tapu Fini, Pelipper, Rotom-W, Gastrodon) AND fulfills our concept AND obeys our celebratory restrictions without a secondary typing to help it stand out and rise above the pack.