Fun thing: Ralph went Method for Galactus.
No, not becoming a planet-devouring overlord. Not sure even Dan Day-Lewis would go that far.
But he did do his mocap in the full, practical Galactus armour - which was apparently heavy as all hell.
He also described a new technique I've never heard of before. He was shot with an ultra-HD camera on an all-white set, bathed in very bright white lights (which made that armour get very hot.) That footage can then be blown up to giant scale without losing detail and digitally matted into real or virtual scenes. So, in effect, he was a human miniature prop. He rather liked that idea.
He also practiced lines while standing on top of the tallest buildings he could find, to get the perspective of belittling pathetic Earthlings.
As the man says, it's not easy to talk down to a small X of gaffer tape on a studio floor, so you've got to have your mind in the right place...