This tool generates strange text with markings on the characters that often makes it hard to read and look like it's spoken or written by some sort of demonic/satanic creature or beastly abomination... at least that's what it looks like to me.
You can control the "weirdness" using the slider in the second box. If you put it really high it may lag out your computer a bit - just to warn you.
It's generated using the Unicode standard which specifies a system for adding diacritic marks to characters. Lunicode.js is the software that makes this demonic text so easy to generate.
Note that some websites may have banned excessive use of diacritics so you text may not be properly displayed on those websites, but a surprising number of big social media platforms still allow it. This is sort of surprising because this sort of text can often be so glitchy that it makes the page look broken.