Too much candy…

Dash, if you can hold Pinkie, you can stand up. Come on, stand up! Lazy pony!

“That, my friend, is because I’m so full of mercy.”

She needs the extra muscle density to carry things in her hair. Cannons, Gummy, prank supplies, party supplies, costumes, etc.

Because the brain requires an extensive life support system along with accompanying organs and tissues adapted to have those life support organs survive in a world where other creatures with similarly designed systems are attempting to eat ponies for nutrients to support those systems.
 
In the most fundamental sense, a person could weigh a few pounds if you only counted the brain and maybe central nervous system (if you count the CNS as part of “who someone is”, things like muscle memory). So is it accurate to say Pinkie weighs 200 pounds or so or is it more accurate to say Pinkie’s body weighs that much?

3 6 infinite corn cakes.

.

All that sugar goes straight to her ethereal void. >:3

“Duh! I live and work in a bakery!”