6 Jokers is a popular online slot developed by Pragmatic Play.
At every spin, one reel is chosen randomly to be a Joker Reel and it is marked.
Every time a tumble resulted from the same spin happens, one more reel chosen randomly from reels that are not currently Joke marked, is also marked.
Only when all the reels become marked, on the next tumble Wild symbols with random multiplier can randomly hit.