Book of 99
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Book of 99 Slot Review

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How to play Book of 99 mobile slot

This Book of 99 slot may have 10 paylines over 5 reels, with Wilds, Free Spins, and Expanding Scatter Pays… but it also has an RTP of 99% and that’s worth shouting about.

Relax Gaming knows what they are doing with this Book of 99 mobile slot machine. They are hoping that you are a fan of mobile slot games that came before it, like the Book of Ra Deluxe slot, or maybe read the Book of Dead slot review.

They are not exactly rewriting history here, but they are making enough tweaks to make you sit up and pay attention. For one the ancient greek slot theme stands out with it’s bold character designs that are instantly eye-catching against the grey colosseum and Ace to 10 low-paying symbols.

For two it’s the only “Book of Game” that lives up to it’s name by giving you a 99% RTP (rather than the much lower 95%) and still keeps the top win of 5,000x your bet. So how exactly does it do that?

Two ways to trigger the free spin bonus

Normal Book of’s, like the Book of Babylon or the Book of Tut slot, will trigger the free spin symbol with the Wild that is also a scatter. 1 or two act as wilds, but 3 triggers 10 free spins.

This is still true in this Book of 99 slot review, and it’s also true that during the free spins one of the symbols will be randomly chosen to act as an expanding scatter pays.

That means that the symbol will expand and cover the reel. More importantly, it will also pay like a scatter – meaning you’ll get a win on all the paylines, regardless of whether the symbols are next to each other on adjacent leftmost reels.

It’s a fun feature that makes these games the only ones that can allow you to get 5 of kind wins on all 10 paylines spin, after spin, after spin, and feel like that 5,000x your bet top win is just around the corner.

Collect 99 Books in the Book of 99 slot

The reason why we believe that this online slot game has an RTP of 99% is that there’s a second way to trigger the free spins – and that’s simply by collecting those wild scatter symbols in the base game of the Book of 99 online slot.

When you get to 99, you trigger the free spins. Nothing else happens, it’s not a special bonus, just the same free games with expanding scatter pays.

But there is a thrill to watching those books get collected and get closer and closer to triggering the magical bonus that has all the big wins of the game.

Because the RTP is high though, the free spins tend to be hit more often but without the same kind of punch as a Book of Ultimate Infinity slot or Book of Ra Deluxe 10 slot. Still, it’s a price we are willing to pay for a real money slot machine that simply pays out more to players overall.

Game Screenshots

Book of 99 slot stats

Mobile Slot releasedMay 2021
Slot typeVideo Slot
SoftwareRelax Gaming
Slot reels / paylines5 Reels / 10 Paylines
House edge / RTP1% / 99%
Slot volatilityHigh
Min/Max bet0.10 / 100
Max win5,000x your bet
Free spins10 Free Spins / Expanding Scatter Pays
Bonus roundsWild Scatter, Free Spins, Expanding Scatter Pays
Slot ThemesAncient Greece
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Bonus Features

Wild Scatter: The Book of 99 is both the wild symbol and the scatter. As the wild symbol can be used to replace any other symbols on the reels to create a win. It can also be collected. As a scatter, when three or more appears, it triggers the bonus games.

Bonus Spins: Get 3 book scatters or collect 99 books, and you'll win 10 free spins. One special symbol will now be chosen to act as an expanding scatter pay. That means that it will expand to cover the reel and pay regardless of where it lands.

Collection: There's a collection meter by the side of the reel. For every wild symbol that shows up in the game, the collection meter will go up by +1. When you hit 99 books, you will trigger the free spins.

The bet of the free spins will be played at the average over the rounds it took to collect the books. So if you like to use slot strategies to up or down your bet, bear this in mind.


  • High 99% RTP
  • High 5,000x stake maximum win
  • Free Spins with Expanding Scatters
  • Low 0.10 minimum bet


  • Takes a while to hit the free spins

Book of 99 Review Conclusion

It's hard not to enjoy a Book of Game that boasts a 99% RTP.

That's high, especially as we don't have to sacrifice the top win of 5,000x your bet or have to jump through multiplier hoops like in the Amulet of Dead slot game.

Book of 99 is a 5 reel 10 payline slot machine with a wild that is also a scatter, and free spins that has one expanding scatter pay symbol. It adds a 99% RTP and a second free spin trigger just for the joy of the spin.

At heart, however, this Relax Gaming slot keeps to the winning formula, and it works all the better for it.

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Review by Lucky Mobile Slots, last updated: May 17, 2023 - Rating 4

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