Yep, seconding this, I don't know if we are expected to put on the riddle solver hat on in order to understand that Matryoshka Dolls is also a key part of making it make sense inside of the logic of comparing lists and finding a criteria in order to iterate them. But I personally just feel as though the instructions are extremely unclear.

I believe it's fixed, but it's difficult to tell the difference.

I believe there's a typo in the formatting of the description?

0000 Start at 0
0011 Switch bits 1,2
0101 Switch bits 2,3
0110 Switch bits 1,2
1001 Switch all 4 bits
1010 Switch bits 1,21100 Switch bits 2,3
1111 Switch bits 1,2

Should be:

0000 Start at 0
0011 Switch bits 1,2
0101 Switch bits 2,3
0110 Switch bits 1,2
1001 Switch all 4 bits
1010 Switch bits 1,2
1100 Switch bits 2,3
1111 Switch bits 1,2

Correct?

OP solved it, closing

+1 to this, I'm pretty sure that an optimal path for it can be less than 4 steps.

and what do you make of [5, 4, 3, 5] ? it's separate from the other two

You have a bug in your code that's not a kata issue. Look again at the last two lines of your code.

There are issues with the description or with js tests, but they're already posted below.

Javascript version needs a revision, literally the exact same value that is to be expected is being printed out but the assertion is marking it as a fail. Frustrating to say the least. Even looking at the other solutions just brings more questions.