How do the Stream Mystery Gifts work?

I'm also trying to figure this out.

I know that when there is a baron steal or pentakill the chances for legendary skins and lcs skins to appear when you buy a mystery skin increases, but I don't know if there is something else related to the stream

Edit: there are people spamming the chat with "!mysterygift" but it's nothing but people trying to get banned apparently

Following the series for the amount of baron steals that occur (I believe Pentakills too), the chance for legendary and esports skins will increase for mystery skin purchases. There was one day in the group stage where 4 baron steals occurred in a single day thus increasing the chance by 4 times.