Okay so I've located a bug I think?
If you switch the house cup for the cute plant, you'll die and also you lose your plant (very sad)... however you still get to keep the house cup, but I'm not sure where to go from here, as you can also put the house cup back and then you're stuck.
I have also yet to figure out what the fish or the yarn is for, nor why you need to give the hippogriff the snacks.
Bonus random question, why are there two different places where you can pick up the snack item?
Okay so the cute plant is the thing that replaces the house cup so you dont die. Once you have the house cup you want to visit the Great Hall and there will be a celebration.
The fish and yarn are not for anything. They were just an added thing I put in there for fun just like the Twilight book.
The snacks are for petting the hippogriff successfully otherwise you'll be harmed and possibly sent to the Hospital Wing. As for why are there two different place where you can pick up a snack item-- just because. lol
Thanks for playing! I hope you had fun!