grammar

Please tell me if this sentence is grammatically correct.
I made pancake. Not so yum yum but easy and fun. What confuses me is the subject yum yum refers to isn't what easy and fun does. So...
Thanks.

You can either say "I made pancakeS" or "I made A pancake."

I personally wouldn't use "yum yum". Try "yummy" instead.

The reason you're being confused is because "yum yum" is NOT the subject of the second sentence at all -- it's an adjective DESCRIBING the subject. The subject is "pancake". This is what is called an implied subject -- you know what it is because you introduced it in the FIRST sentence. Technically, the second sentence is more of a sentence FRAGMENT because it doesn't spell out the actual subject, but that's okay, because it's still how people actually talk.

Hi, I know what you mean. However, if pancake was the subject of the 2nd sentence, don't you think pancake was easy and fun doesn't make sense? That's what concerns me most. Thank you.

Easy and fun don't refer to the pancake; they refer to MAKING the pancake.

Strictly speaking it's not grammatically correct.
I made pancake.
If you skip the article it sounds like your job is to make pancake. And you only make ONE pancake. A very peculiar job.
Like Uriel said, the second phrase lack subject and verb.
I made a pancake. It was not yummy. Making it was easy and fun.
Then you may want to use conjunctions to connect them.