Workshop

it would be great if it weren't for the hamsters. old joke.

I remember hearing about killer hamsters somewhere... let's make them guinea pigs instead.

can it be used? when and how many times?

It can be used once, on the following night after the theft. The player whose artifact was stolen cannot use it on that night.

does it take a night to upgrade the skill?

Yes.

do the rogues kill together or one by one?

Together, but the clue is given for one.