"This is an ordinary cat."

Translation: Ini kucing biasa.

[NerdAlbert]

I dunno Duo... that cat looks kinda sus..

[haocha22]

Does reversing the first two words make a difference ie. Kucing ini biasa?

[joeldipops]

Yes.
"This cat is ordinary" vs. "This is an ordinary cat"

[Mal205614]

but they both mean the same in English! Care to explain why you think there is a difference?

[Rick392366]

The grammar is different.

Here is more info :

'ini' , 'itu', Tips & Notes, Addendum.
https://forum.duolingo.com/comment/31492712

Adjectives, Noun Phrase, Tips & Notes, Addendum.
https://forum.duolingo.com/comment/31285942

[joeldipops]

They emphasise different things and would be used in different situations.

[Mal205614]

"kucing ini biasa" should be accepted too

[AVAX3M]

It should not. "Kucing ini biasa" would be "this cat is ordinary".

[ben.toth]

"Ini ada kucing biasa" is marked wrong, but I'm not sure exactly why? Is it just not an economical way to say that phrase?

[Rick392366]

"ada" cannot be used like that.
If you want to use a verb in the Indonesian sentence, then "adalah" can be used here.

Here is more info about the use of "ada":
https://forum.duolingo.com/comment/29750475

Here is more info about the use of "adalah":
https://forum.duolingo.com/comment/29750500

[joeldipops]

Ada doesn't work like "is". It basically means "exists". I'm not sure if "ini ada kucing biasa" is grammatical, but even if it is, it certainly changes the meaning.