What happens when All Myths Are True is turned Up to Eleven? You get a Fantasy Kitchen Sink! Everything is true, even if it comes from vastly different origins. So not only are there really fairies, there are ghosts, vampires, werewolves, mummies, Sea Monsters, giant worms, superhuman Mutants, zombies, aliens, time travellers, espers, angels, demons, God, Jerkass Gods, Evil Gods, Lazy Gods, Eldritch Abominations, Precursors, magic, psi, chi, and so on. Generally a sure sign of it is when creatures from typically different genres (aliens, vampires, fairies) all exist within the same world with individual origins of their own, each implausible in their own way -- leading up to a long series of suspensions of disbelief rather than just one.