Casual usage of i-adjectives and ending particles

Question

In Real casual japanese one may hear

明日のテストってこわ。。。

I am wondering, how often this level of 'casualness' happens.

Can I add sentence ending particles, even though there is an い omitted (and です). For example:

ゆきは走るのがはやね。

I omitted the whole structure, but still added ね to emphasize, that Yuki runs fust, doesn't he?

However this is pretty standard, for a plain form, am I right?

おもしろいね

If a similar question has been answered somewhere, please link it for me, and also I'm not sure if my question is phrased correctly, I hope it's understandable.

Answer 1

ゆきは走るのがはやね is impossible.

Those stand alone stems of i-adjective are not so much a casual form as a kind of interjection you use when you are surprised and it doesn't allow any grammatical elements to follow. In addition, it's different from collapse of diphthongs.

Answer 2

There are several patterns for adjectives in casual speech:

One is that the end of the adjective changes to an "e" vowel, like おもしれー, はえー, おせー, こえー, いてー.

One is that the end of the adjective changes to an "i" vowel, like さみー,あちー,ねみー, かいー.

One is that the end of the adjective is omitted, like さむっ, あつっ, くさっ.

Some particles like な, よ, か can be added to them (except for in the omitted ones), like おもしれーな, ねみーよ, さみーか but ね isn't usually added to them.