Santastic 4

When a stacked wild appears, it moves from right to left until it eventually disappears. Throughout the same spin, additional stacked wilds can also appear. If you land 3 or more bonus symbols, you will be awarded 8 Free Spins, during which random frames are added to the grid before the spins commence. Each time a new wild lands, more frames will be added, and once an entire reel is filled with frames, it triggers the walking wild and the re-spins feature. In the Free Spins mode, walking wilds may appear with a multiplier of either x2 or x3, enhancing the pay outs on the active winning lines during the re-spins.