You will see a large, locked alien (the blob) in a spaceship in the centre of the Blob Clusterbuster reel set. At the beginning of every spin, a ring of lights around this symbol is inactive. Lights are activated when a winning cluster is formed adjacent to them. Fill all the lights on one spin, and features will be triggered.
The first triggering of the cluster buster will result in lower-value symbols being upgraded. If you trigger the cluster buster again at any point, you will reach level two, where random wilds are added to the reels. One more trigger of the cluster buster and high value and wild symbols will expand to 3x3 on the reels, helping to form bigger clusters.
Trigger the cluster buster a fourth time, and you’ll enter the Invader Spins game.