Book of Monsters

Today, our leisure activities have changed a lot, but some things are coming back in a new form. For example, the Book of Monsters slot machine from Pragmatic Play, released in March 2025, allows us to rediscover bizarre and fun little monsters that remind us of our childhood.

Looking back less, they also inevitably remind some players of the monsters from Play N Go’s Reactoonz series. To describe them simply, they have a mischievous look, not exactly scary but rather funny, and they roam what appears to be a cave illuminated by a blue glow. The environment is also populated by ghosts, creating a pleasant, spooky atmosphere, far from terrifying.

In the midst of all this, there’s the famous Book of Monsters. It might be reminiscent of traditional “Book of” games, with their symbols expanding to cover the reels during Free Spins. But this time, the concept is different. The book opens to reveal Free Spins and randomly selected symbols. These can grow during the bonus feature thanks to a progressive feature that evolves as special symbols are collected. A mechanism that ultimately stands out from what we’re used to seeing.

The colossal symbol expansion system allows the selected symbol to increase in size during the Free Spins.

The Book of Monsters slot machine is played on a 7×7 reel grid powered by the Cluster Pays mechanic. Featuring high volatility, this slot offers an RTP of 96.50% and can pay out up to 5,000x the bet. You can bet between $0.20 and $480 per spin, with the option to activate the Ante Bet, which gives you seven times more chances to win access to the Free Spins.

In the base game, your only concern will be to form blocks of at least five or more identical symbols connected horizontally or vertically. Furthermore, in the base game, on any spin, symbols can randomly cover 3×3, 4×4, 5×5, 6×6, or 7×7 positions on the game screen. The red, green, and purple monsters pay the most, with payouts ranging from 0.50x to 5,000x the bet. They are complemented by the A, K, Q, and J symbols, which can pay between 0.20x and 250x the bet. There’s also the bonus symbol, which can pay between 2x and 100x the bet when you find 3 to 7 of them in the game.

Free Spins are the only feature in Book of Monsters. This bonus is preceded by a Gamble mode allowing you to collect more free spins or obtain a better magnifying symbol. During the bonus, a progressive feature will allow you to collect special symbols, making them grow as you progress through the levels.

Free Spins

Find 4, 5, 6, or 7 bonus symbols to trigger Free Spins and win 5, 6, 7, or 8 free spins, respectively. First, a random symbol will be selected to be the Fat Symbol for the following spins.

Before the bonus begins, you can bet separately to increase the value of your selected Fat Symbol to the next highest value or bet to increase the number of Free Spins. You can also choose to collect the current Fat Symbol and the number of Free Spins and start the bonus at any time.

If you choose to bet to upgrade the Fat Symbol, a page of the book will turn and the next high-value symbol can be revealed, unless the book reveals “The End” page, ending the bonus before it even begins. If the symbol is revealed, the Gamble feature is won and the Fat Symbol is upgraded to the next one.

If you choose to bet to get more Free Spins, a page of the book will turn and the next number of Free Spins will be revealed, unless the number of Free Spins is revealed, the Gamble feature is won and you will upgrade your number of Free Spins to the next value.

The odds of winning in the different Gamble options depend on the current number of Free Spins and the selected Fat Symbol. This percentage chance is listed below each Gamble option.

The Free Spins then start when you choose to collect the current number of Free Spins and the current Fat Symbol, or when the maximum Gamble feature has been reached.

Once the bonus feature starts, the Fat Symbol will occupy a 1×1 position and will always be present on the screen, moving from one place to another with each spin. All instances of this symbols that land on the grid during a spin will be collected in a counter, and when a certain number of symbols are collected, the Fat symbols will grow to cover a larger area.

Collect 30 Fat symbols to reach the second level and have the Fat symbol cover 2×2 positions. Collect 27 more to cover 3×3 positions, then 24 more to reach 4×4 positions, then 20, 16, and finally 12 more to reach the next levels so that the Fat symbol covers 5×5, 6×6, and 7×7 positions.

Each time the Fat symbol increases in size, you will win 1, 2, or 3 Free Spins randomly.

Book of Monsters vs. 3 different slots from Pragmatic Play

Buy Bonus

Free Spins can also be accessed instantly through the Buy Bonus option, which costs 100x the total bet. By purchasing access to the Free Spins feature, you will receive 4, 5, 6, or 7 random bonus symbols.

Collect these creatures from the Book of Monsters

The Book of Monsters slot machine doesn’t really work like a classic slot using the “Book of” mechanic, but there are still similarities. Here, the book opens to award a certain number of free spins and a randomly selected symbol. These parameters can be significantly improved before the bonus round thanks to the two Gamble features. While starting with only 5 free spins isn’t necessarily incredible, it can be useful. Similarly, it can be a good idea to bet on the special Fat symbol so that it reaches a higher value; this will be very useful during the bonus round. It can gradually grow as you collect the same symbol, and this will help you access bigger rewards, up to 5000x the maximum bet if you completely cover the grid with the red monster symbol.