"This tastes bad."
I'm not 100% sure, but I think if you use これ you have to use は, because you're establishing that これ is the topic, you are going to talk about "this". If you don't use これ (because it may be obvious that you're talking about "this") you don't need the topic particle (は). Please feel free to correct my english or my japanese because I'm just learning :)
You're pretty much correct, but in speech (especially casual speech), it's acceptable to drop the は if the thing you want to be the topic is obviously the topic. So, 「これ、まずいです」 is fine if you're speaking, or writing informally.
Interesting. Thanks for posting or else I would havu thought は was mandatory.
It rejected me when I used the Kanji 不味い. I reported it but then I realized, is this intentional, like because these Kanji are generally not used? Or is this just an oversight. Would it seem unnatural if I wrote these Kanji out?
Not sure if it's intentional. The kanji for "mazui" is not generally used, but I think it should be accepted anyway. As examples, I could find two media occurence of the word. Episode 66 of the anime Digimon Fusion is "おいしい？まずい？デジモン・ラーメン勝負！"¹ and the first episode of the Japanese drama Bartender is "嵐を呼ぶ男VS伝説ホテル王…永久にまずい酒"².
I believe if you use これ ("kore"/this) you have to use は for the full sentence これはまずいです ("kore wa mazui desu"/this tastes bad).
But if it's implied from context so the other person knows what you're talking about you can drop the これ and associated は altogether and just say まずいです ("mazui desu"/tastes bad).
I don't think これまずいです (the full sentence without the は) is technically correct, but I'm learning too so correct me if I'm wrong.
It's fine to drop the は after これ when speaking casually, but I wouldn't expect Duo to accept it!
You don't need the です, since まずい is a verbal adjective. です serves to make the sentence more polite, but it's not needed gramatically.
kono, sono, and ano must be followed by a noun immediately after. they need a noun to specify. for example: " あの人は誰ですか？" the あの is followed immediately by 人, which is the noun. you're specifying that you want to know who THAT person is. - kore, sore, and are are followed by " は " normally. it's a broad way to describe objects. for example, " このももはいくらですか。" is asking how much specifically that peach is, and if you used " これはいくらですか。" you're just asking about a non-specified object. i don't think you would use something like ” これはももがいくらですか。” i hope this makes sense! i'm also only a student myself so anyone feel free to correct me.