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Book of 99 is a slot from Relax Gaming, released in 2021. It uses classic Book-style presentation with ancient artefacts, a mystical book, an adventure setting and a high RTP that became the game’s defining feature.

The game grid has 5 reels and 3 rows with 10 paylines. The theoretical RTP is 99.00%, which is noticeably above the average for online slots. Volatility is high, the usual betting range is listed as 0.10 to 100 and the maximum win reaches 12075x the stake.

Game features

• Wild symbols
• Scatter symbols
• Free Spins
• Expanding Symbols
• Bonus Meter
• Symbol Collection

The main special symbol is the Book. It has two functions: replacing regular symbols as a Wild and triggering Free Spins as a Scatter. When 3 or more Book symbols land, the Free Spins bonus activates.

The game also has a Wild-symbol collection meter. Every Book/Wild that appears is added to the Bonus Meter. When the counter reaches 99 collected symbols, the player enters the bonus even without the standard Scatter combination.

Bonus mechanic

Free Spins are the key feature in Book of 99. At the start of the bonus, a special symbol is selected and can expand across the reels during the free spins. If enough of that symbol lands, it expands and helps create additional payouts on active paylines.

Expanding Symbols make the bonus mode the main source of large potential. A particularly strong result is possible when one of the high-paying symbols is chosen as the expanding symbol.

The Bonus Meter adds a long-term target. Even when the bonus does not trigger immediately from 3 Scatters, every collected Wild moves the player closer to the next Free Spins round. This makes Book of 99 feel more progressive than many classic Book slots.

Theme and style

The slot uses an adventure style inspired by ancient treasure, a mystical book and classic Book of machines. Its reels feature characters, artefacts, the Book, card symbols and special bonus icons. Book of 99 belongs to the following categories: Egyptian slots, Book slots and video slots.

The visual design remains clear and traditional: a 5×3 grid, 10 paylines, large symbols and a familiar bonus structure. The focus is not on complex mini-games but on the high RTP, Book collection and Free Spins with an expanding symbol.

Popularity among players

Book of 99 is popular with players from the United Kingdom, Canada, Germany, the Netherlands, Norway, Sweden, Finland, Denmark and New Zealand. It may appeal to users who enjoy Book-style mechanics, a high RTP, Free Spins and a simple structure without overloaded additional modes.

The slot may suit players who prefer high volatility, fixed paylines, a Wild/Scatter Book and a bonus round whose main potential comes from expanding symbols.