Some fossil Pokemon revived or hatched in Galar will have new regional forms and/or gigantamaxes.
Gigantamax Aurorus will have two extra heads made of ice in tribute to Godzilla's rival Ghidorah.
Galarian Bastiodon will be offensive instead of defensive, with its "shield" being redesigned into a cow catcher shape.
Yamper's third stage is blue and it becomes electric/water. It's a Sherlock Holmes reference.

Finally, Diamond and Pearl's underground will return and be greatly expanded upon, with online features for the first time ever!