Book of Monsters: Slot Overview

The title could pass for some harmless bedtime reading at Hogwarts School of Witchcraft and Wizardry, yet Pragmatic Play’s Book of Monsters is, in reality, a cluster-paying grid slot. It isn’t a classic ‘Book of’ game where a special symbol expands to fill its reels; instead, books open to trigger free spins and to pick symbols at random. Those selected symbols do expand during the bonus, though the behaviour is closer to Fat Rabbit than to Book of Dead.

Despite the monster theme, the creatures on the reels and on the book don’t come across as under-the-bed terrors or true villains. With their big eyes and toothy smiles, they lean more toward a Reactoonz-style look—more playful troublemakers than anything genuinely sinister. The action takes place in a cave which, granted, features eerie, glowing-eyed spectres, washed in blue lighting that turns more orange when free spins land. Ideally, you’ll see plenty of orange, since Book of Monsters’ biggest moments are more likely to arrive in the bonus round.

Set on a 7×7 grid, Book of Monsters uses a cluster pays mechanic, paying when at least 5 matching symbols connect next to each other vertically and/or horizontally. The base game offers very little in the way of extras, so players either purchase the bonus or enable the ante bet to make free spins 7 times more likely to trigger. Stakes range from 20 c to $/€240, and switching on the ante bet doubles the wager. With high volatility, the best RTP available across all options is 96.5%.

Lower-value symbols are card ranks paired with suits—like the jack of diamonds, the queen of clubs, the king of hearts, and the ace of spades. Above them sit a purple, green, and red monster. A 5-symbol cluster pays 0.2 to 2 times their stake, rising to 100x to 5,000x for a 49-of-a-kind cluster. There are no wilds, but at random in the base game, so called fat symbols sized 3×3, 4×4, 5×5, 6×6, or 7×7 can appear.

Book of Monsters: Slot Features

Landing 4, 5, 6, or 7 scatters in the base game grants 5, 6, 7, or 8 free spins. With the ante bet turned on, hitting 3, 4, 5, 6, or 7 scatters instead awards 4, 5, 6, 7, or 8 free spins, in that order.

After that, a random pay symbol is selected to serve as the Fat symbol for the bonus. Players can choose to gamble the Fat symbol in hopes of upgrading it to a higher-paying one. They may also gamble to increase the number of free spins. Alternatively, they can collect and begin the feature immediately. If a gamble is taken for spins or a better Fat symbol and the book shows ‘The End’, the bonus round stops on the spot. If not, successful gambles can award up to 8 free spins, and the Fat symbol can be pushed up to the top-value symbol.

The free spins feature includes a progressive feature built around the Fat symbol. When the round begins, the 1×1 Fat symbol is always on the grid, and it shifts to a new position at every spin. Any symbols of the Fat symbol’s type that land during the round—provided they aren’t covered by the Fat symbol—are collected by a meter. When the meter reaches certain totals, the Fat symbol grows in size. Gathering 30 symbols upgrades it to 2×2, collecting 27 more turns it into 3×3, collecting 24 more makes it 4×4, collecting 20 more makes it 5×5, collecting 16 more makes it 6×6, and collecting 12 more makes it 7×7. Each time the Fat symbol increases size 1-3 additional free spins are awarded.

Bonus Buy

The free spins bonus is available to purchase from the base game for 100 times the bet. When activated this way, 4, 5, 6, or 7 scatter symbols are randomly placed on the triggering spin.

Book of Monsters: Slot Verdict

In the brief moment between seeing the name and checking the rules or watching it play, it’s easy to assume Book of Monsters will deliver another round of Book of Dead-style expanding-symbol action. But the old advice about not judging a book (or a ‘Book of’ slot) by its cover applies here, because it quickly becomes clear Book of Monsters isn’t that kind of title. Still, it can feel a bit like one of those TV episodes assembled from a string of short clips from earlier seasons—several elements will seem familiar.

The most obvious callback is the ‘Book of’ nod, and while the gameplay differs, the books still handle free spins and the selection of a random special symbol. Beginning with 5 free spins isn’t exactly generous, which can make the gamble option pretty appealing. In testing, 5 spins could be enough to level up the Fat symbol—though not to the maximum—so having more spins is clearly beneficial. Also, the Fat symbol isn’t wild, so chasing a higher-paying Fat symbol via the gamble can be tempting too. On the other hand, lower-paying symbols tend to appear more often on the grid, which can make growing the Fat symbol easier than relying on a rarer premium—so it comes down to gambler preference.

Without a multiplier mechanic like Royal Potato and with no expanding wild in the style of Fat Rabbit, Book of Monsters can feel somewhat restrained. Even so, it carries a win cap of 5,000x (the same as landing a 7×7 version of the top-paying symbol), and the 1 in 547,945 hit rate isn’t surprising. Overall, Book of Monsters is a slightly odd patchwork of ideas, and the base game can be a touch flat, but the roaming, growing Fat symbol is entertaining enough to make it worth a look.