'become scary' is correct and usable in written English.
You can use it to describe something that has suddenly become frightening or intimidating. For example: After the loud boom of thunder, the dark night suddenly became scary.
[C4.] FRIGHT RETURNS Marketing campaigns for Halloween have become scary again, continuing a trend from the last couple of years.
"Novartis is scary; Merck could become scary, Teva as well," Ms. Kulhoff said, noting the threat they pose to the companies that do the initial development of biologics.
In an e-mail on Jan . 30 , 2012Mr. Iksil, who earned the nickname the London Whale for his outsize bets, wrote to his manger, Javier Martin-Artajo, that the strategy had "become scary" and the "upside is limited unless we have really unexpected scenarios".
"It's become scary to fly now," said Nina, 19, a university student sharing a fast-food dinner with a classmate.
As you get older, the unknown can become scary as you question more and more things in the world, slowly losing that childlike innocence we all once had.
Sex, in general, has become scarier to us than ever before.
Moments of everyday chaos commotion in a movie theater, or a weird clatter in the furthest corner of my office have become scarier lately.
And this is when technology becomes scary.
"It becomes scary for dictatorial governments after their ideas are challenged and artists can really attract attention".
These and similar texts became scary samizdat in BBC newsrooms while, inside the BBC, a handful of influential figures, including Richard Sambrook, then Director of News, urged change.
