Book of the Priestess Slot by Evoplay

The book-of formula gets an Aztec spin here, with the golden Book acting as both Wild and Scatter. Three or more Books trigger 10 free spins and randomly select one regular symbol to become the Expanding symbol. When enough of that symbol land on the reels, it stretches to fill all three rows on its reel - and it forms combinations even across non-adjacent reels, which is unusual for the subgenre.

What separates this from a standard book slot is the Ancient Mask counter. During free spins, every Book symbol that lands charges the mask by one tick. The counter starts at 7 and counts down to 0. Hit zero and the game awards an additional Expanding symbol plus 5 extra free spins, then resets the counter back to 7. This cycle repeats until either all 9 regular symbols become Expanding or the free spins run out.

The math behind a full unlock is aggressive. The Priestess symbol pays 500x bet for five of a kind, and that payout gets multiplied across multiple expanding reels when several symbols are active. With all 9 symbols expanded, nearly every reel combination pays something. Getting there requires sustained Scatter landings during the bonus - each one needs to keep feeding the mask counter while the round is still alive.

The paytable has a steep drop between the top symbol and everything else. Symbol 1 (Priestess) pays 500x for five, but the next tier drops to 200x, then 75x. Low symbols cap at 15x for five. That gap makes the expanding symbol selection at the start of free spins a make-or-break moment - landing the Priestess as your first expand sets up entirely different win potential than getting a low card.