Book of Darkness ships with a 5-reel, 3-row reel grid with 10 paylines. I played 320 spins at a 1.00 stake, starting from a balance of 1,000.00 credits. It ships with a bet amount spanning from 0.10 - 10, and the top bet is a little modest. The balance never rose above its starting 1,000.00 and bottomed out at 837.50.
There are 10 symbols all in all available in this slot, the wild counted, and beginning from lowest value these are - Q, K, A, potions, daggers, crystals, rings, dark wizards, huntresses, and the book. The book is both the Wild and the Scatter, and as a Wild it stands in for every regular symbol except the Huntress and the Dark Wizard. The paytable can seem a little confusing. The Huntress, Dark Wizard, Ring and Crystal pay from two of a kind, while every other symbol needs three. But payouts are calculated left to right on 10 fixed paylines when the symbols connect to create a win, so for instance, a line of five of the highest paying line symbol pays a 25x win. That symbol is the Huntress or the Dark Wizard. Four of either pay 10x the stake, three pay 2x and two pay 1x.
In truth, I managed to hit a 59x win while running my testing. It came on spin 225 and lifted the balance to 955.10. That was outside of the bonus. Huntress, Book and Dark Wizard in a straight line on adjacent reels, in either order, trigger the Clash for Power feature, which can lead to Shadowform free spins, and I did not draw it in 320 spins.
The count of free spins is decided by the quantity of Book of Darkness symbols, and additional books give extra spins. Three books also pay 2x the stake anywhere on the reels, four pay 20x and five pay 200x. During my testing session I got between 10 and 15 free spins. My first two rounds came from three books and the third from four. But it can award up to 20. The feature landed on spins 173, 203 and 284, and the best of those rounds paid 76x the stake.
A random symbol will be automatically chosen before the free spins begin. Any symbol except the book itself can be the one chosen. It will serve as an expanding symbol throughout the round, and it's not possible to retrigger with further free spins.
The Minty Breakdown: Book of Darkness took its return from the free spins, which paid 50% of everything won, and over 320 spins it gave back 82.7% of what I wagered.