Three or more Scatter symbols appear in the reel awards Free Spins. The number of Free Spins is as follows:

Three Scatter symbols award eight Free Spins

Four Scatter symbols award fifteen Free Spins

Five Scatter symbols award twenty Free Spins

Five extra spins are awarded for every two Scatter symbols appearing in the reel during the Free Spins feature. 

Also, Wild symbols might appear during the Free Spins, which substitutes all symbols except the Scatter and Golden Bison symbols. There is a probability that winning multipliers appear on Wild symbols, but the winning multiplier multiplies the winning amount only when they're part of the winning combination.