The word "ocean" can be both countable and uncountable, depending on the context. Generally, when referring to the vast body of saltwater that covers most of the Earth's surface, it is uncountable. However, you can use it in a countable sense when referring to specific oceans, such as the Atlantic Ocean or the Pacific Ocean, in which case you can say "two oceans."
Yes, castle is a countable noun: We have two castles, one castle in the countryside and one castle on the ocean.
countable
countable
The noun 'hill' is a countable noun. The plural form is 'hills'.
cookies are countable unless you have brain problems
countable
Shark is a countable noun.
Duck as an animal is countable, but if you mean the meat it is uncountable.
Prawn - prawns is the plural - is a countable noun
countable
few is countable
Countable