Book of the Priestess Bonus Buy Slot by Evoplay

The Scatter functions as both Wild and trigger - three or more award 10 free spins. Before the round begins, one of the nine regular symbols gets selected at random as the expanding symbol. When enough of that symbol land to form a winning combination, it stretches to cover all three rows on its reel. The expansion happens after standard wins are calculated, so a single spin pays twice: once for the regular hit, then again for the expanded version.

What separates this from typical Book of Dead-style games is the Ancient Mask counter. During free spins, every Scatter that lands charges the mask by one step. The countdown runs from 7 to 0, and reaching zero adds a second expanding symbol to the pool plus 5 extra free spins. The counter then resets, so collecting another 7 Scatters unlocks a third expander with 5 more spins. Up to 9 expanding symbols are possible in a single bonus round - at that point every regular symbol on the grid expands on contact.

Expanding symbols form wins even across non-adjacent reels, which matters more as multiple expanders stack up. Two or more expanding symbols landing together each expand and pay in sequence. The buy bonus costs 87x total bet and starts the free spins with one random expander and the Ancient Mask active from spin one.