File it with the footgun of the two different array slicing syntaxes: https://c3-lang.org/language-common/arrays/#slicing-arrays

I have already opened a discussion about this with the author, and I must say I agree to disagree that a language needs arr[start..end] (inclusive) as well as arr[start:len] (up to len-1) and if you use the wrong one, you’ve now lost a foot and your memory is corrupted.

The closed intervals for slices caught my eye as well, but I simply filed that under 'that's a weird quirk' rather than 'wtf?'.

It would require more thinking on my end to change that to either 'this is an acceptable choice' or 'this is a terrible idea'.

But the array indices being reversed on declaration? I cannot think of an upside to that at all.