In this game it is all about entering one of the two bonus rounds available in the game. Bonus rounds aside, there is only one feature in the base game. On any spin one reel has a chance of being highlighted. Any wilds landing on the highlighted reel will expand, increasing your chance of connecting winning pay lines.
Skull of the Abyss is one of the two bonus features. This is triggered by landing three Skull of the Abyss scatter symbols. This is a pick feature, you will keep picking skulls until you receive one of the end symbols granting you a big bonus or entry to the Doom Spins bonus round