Book of Monsters Slot Review
A shaggy pink book-creature with mismatched googly eyes floats over a stone cauldron, bubbling turquoise smoke, while a one-eyed red monster lounges across the signboard beside the reels. That’s Book of Monsters, and Pragmatic Play have made the odd decision to put almost everything this game has into a single bonus round, leaving the base game to get by on charm alone.
The numbers are solid rather than spectacular: 96.50% RTP, medium volatility, cluster pays, and a 5,000x win cap.
It sits in familiar company alongside Sugar Rush and Gates of Olympus, both of which run large grids and escalating symbol mechanics. Fire Portals is the closer comparison, with its own symbols that grow across a round.
Cluster Pays on the 7×7 Grid
Wins form in blocks of five or more matching symbols connected in either direction, and only the highest win per combination counts. Multiple blocks in one spin all pay, and everything is multiplied by the base bet. There’s no wild in this game.
The only symbol outside the standard set is the eye-icon BONUS symbol, which triggers free spins and pays on its own from three appearances. The paytable is a steep ladder, and the top prize needs a near-full grid:
- Red monster – 5 symbols pay 2x, rising to 500x for 40-48 in a block and 5,000x for 49
- Green monster – 5 pay 1x, up to 500x for a full 49-symbol grid
- Purple monster – 5 pay 0.5x, up to 250x for 49
- A – 5 pay 0.4x, up to 200x for 49
- K – 5 pay 0.3x, up to 150x for 49
- Q – 5 pay 0.25x, up to 125x for 49
- J – 5 pay 0.2x, up to 100x for 49
- BONUS – pays 2x for 3, 5x for 4, 15x for 5, 50x for 6 and 100x for 7
The mid-tiers matter more than the endpoints suggest. Between 9 and 12 red monsters in one block pays 15x, and the ladder steps up through every bracket from there, so a 30-symbol premium cluster is already a serious result without touching the top prize.
During the base game, any spin can drop a mega block of 3×3, 4×4, 5×5, 6×6 or 7×7 symbols onto the grid at random. It’s a simple addition, but on a cluster-pays grid a 5×5 block of premiums is close to a guaranteed big hit. Those spins carry real weight.
Free Spins and the Progressive FAT Symbol
Triggering the round
Four, five, six or seven BONUS symbols award 5, 6, 7 or 8 free spins respectively. Before the round begins, a random paying symbol is selected as the FAT symbol for the whole round.
The gamble
You can then gamble before collecting. Two options are on the table: turn the book’s pages to upgrade the FAT symbol to the next higher value, or gamble for more free spins.
Each page either reveals the upgrade or shows THE END, which loses the gamble and ends the round with nothing. Gambles can push the round up to 8 free spins or to the red monster as the FAT symbol.
Your chances on each option shift with how many spins you already hold and which symbol is currently selected, and the odds sit next to each button before you commit. Collect at any point, or reach the gamble limit, and the round starts.
Growing the FAT symbol
The round itself is a collection game. A 1×1 FAT symbol sits on the grid and moves to a random position every spin. Every instance of the selected symbol that lands without being overlapped by it goes into a meter. Hit the thresholds and the FAT symbol grows:
- 30 collected – grows to 2×2
- 27 more – grows to 3×3
- 24 more – grows to 4×4
- 20 more – grows to 5×5
- 16 more – grows to 6×6
- 12 more – grows to 7×7, filling the grid
Every size increase also awards 1, 2 or 3 extra free spins at random, so a round that keeps levelling up keeps feeding itself. Special reels are in play during the feature.
The design gives the round a visible trajectory. You can see how close the next growth is, and a 7×7 FAT symbol of any paying symbol is the whole board paying at once. If the total win reaches 5,000x the bet, the round ends immediately with the cap paid out.
Ante Bet and Bonus Buy
Ante Bet
Switching the bet multiplier from 20x to 40x lowers the trigger to just three BONUS symbols, which makes the feature seven times more likely to hit naturally. The RTP stays at 96.50% either way.
Two things change when you use it. Four BONUS symbols now award only 4 free spins rather than 5, and the bonus buy is switched off entirely while the Ante Bet is on.
Buy Free Spins
The round can be bought outright from the base game for 100x the base bet. On the triggering spin, 4, 5, 6 or 7 BONUS symbols can land, so a bought round can still start with up to 8 free spins.
The buy runs at 96.50% RTP, the same as everything else in the game. Whatever route you take into the feature, the maths doesn’t change.
Our Honest Verdict
Overall Rating: 7.8/10
Playing Book of Monsters is mostly a matter of waiting in a very pretty cave. The monster artwork is excellent, the mega blocks land with real weight, and between them you’re collecting eyes for a bonus round that is clearly the whole point of the exercise.
The free spins round justifies the wait, and it’s the best thing here. The pre-round gamble has readable odds and a real decision in it, and the collection meter means every spin inside the feature counts for something, even the losing ones. The growth thresholds are steep, though, and that’s the weakness: reaching a FAT symbol big enough to pay seriously takes a round that’s already going well, so most bonuses finish modest.
If you enjoy a slow build and don’t mind a base game that coasts, this is an easy game to like. Players chasing big instant hits will find the pacing a slog, and the monsters won’t change their minds.
Book of Monsters FAQs
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What is the RTP of Book of Monsters?
The RTP is 96.50%, and it stays at that figure in normal play, with the Ante Bet on, and when buying the bonus. -
Is Book of Monsters high volatility?
No, it’s a medium volatility game, so payouts range from low to very high and tend to come steadier than in a high volatility title. -
How do wins form in Book of Monsters?
It uses cluster pays on a 7×7 grid. Symbols pay in blocks of at least five connected symbols, with multiple blocks in one spin all adding to the win. -
What is the minimum and maximum bet on Book of Monsters?
Bets run from 0.20 to 240 per spin. -
How do you trigger free spins in Book of Monsters?
Land 4, 5, 6 or 7 BONUS symbols to win 5, 6, 7 or 8 free spins. With the Ante Bet active, 3 BONUS symbols are enough, awarding 4 free spins. -
What does the FAT symbol do?
A random paying symbol becomes the FAT symbol for the free spins round. It starts as a 1×1 block that moves each spin, collects matching symbols into a meter, and grows up to 7×7 as thresholds are hit, awarding 1-3 extra free spins with each size increase. -
Can you buy the bonus on Book of Monsters?
Yes, the free spins round can be bought for 100x the base bet, and the triggering spin can still land 4 to 7 BONUS symbols. The buy is disabled while the Ante Bet is selected. -
What is the maximum win on Book of Monsters?
The maximum win is 5,000x the bet, in both the base game and free spins. Reaching it during free spins ends the round immediately and pays the cap.
