I've left it to the very last days to finish growing our pumpkins because of lingering quests I kept messing up!!
I can't remember if any other Ghostly Critters add pounds to the growing pumpkin when spotted. And if so, how many?
I know the Halloween mice and mallards add 2lbs (4lbs for the pygmy) and the Crow adds 10lbs... but do all the underwater Ghostlies, Merwiches, etc add the same amount of pounds as they give diamonds? Or don't they count at all?
Is there a list anywhere?

All of the ones with "ghostly" or "zombie" in their name, including underwater, plus the crow and merwich.  The weight they give is the same as the diamonds they drop.

Great Tracey! Thank you! I wasn't sure... x

None of the fan sites list this and I forget every year what helps to make a pumpkin or sunflower grow.  For years I never tried to grow a pumpkin spotting ghostly pond wildlife as I didn't know they were included.