Book of 99 is a high-volatility Greek mythology slot from Relax Gaming featuring an exceptional 99% RTP. This 5-reel, 10-payline game combines classic book-style mechanics with innovative Wild Collection features and expanding symbols for maximum win potential of 12,070x stake.
Book of 99 represents Relax Gaming's strategic entry into the crowded book-style slot category, distinguished not by revolutionary mechanics but by an unprecedented return-to-player configuration. While the Ancient Greek theme and expanding symbol features follow established patterns, the 99% RTP figure positions this game as a mathematical outlier in an industry trending toward lower player returns. This review examines whether the exceptional RTP alone justifies attention or if the gameplay mechanics provide additional value beyond the numbers.
Released in 2021, Book of 99 directly challenges the dominance of Play'n GO's Book of Dead and similar titles by offering players a significantly higher theoretical return. The game's title directly references its 99% RTP, making this mathematical advantage the central marketing proposition. Relax Gaming has opted for refinement over innovation, implementing familiar book-slot mechanics while adjusting the economic model to favor player retention over short-term house edge.
The Greek mythology setting provides visual context through comic book-style character designs, including Lamia, a cyclops, and heroic figures rendered in Relax Gaming's distinctive cartoonish aesthetic. The base game unfolds against temple architecture, transitioning to a sun-drenched Arcadian landscape during bonus rounds. Audio design combines rhythmic percussion with melodic elements that establish thematic atmosphere without overwhelming gameplay focus.
The fundamental gameplay follows the book-slot template established by Novomatic's Book of Ra. Players spin a 5x3 grid seeking matching symbols across 10 paylines, with wins calculated from left to right on adjacent reels. The paytable divides into two tiers: lower-value royal symbols requiring minimum three-of-a-kind matches, and premium character symbols that pay from two matching icons.
Premium symbol payouts scale from 75x stake for the lowest character to 500x for the top-tier hero symbol when five appear on a payline. This creates potential for full-screen wins reaching 5,000x stake before feature multipliers, though such outcomes remain statistically rare given the high volatility profile. The game accepts stakes from 0.10 to 100 credits, with all wins calculated as multiples of the total bet rather than per-line amounts.
The low-pay tier consists of stylized 10-through-Ace card ranks designed to match the Greek aesthetic. These require three or more matches and deliver modest returns suitable for maintaining bankroll stability during base game sessions. The premium tier features four character symbols: Lamia (a child-eating monster from Greek mythology), a one-eyed cyclops, a female warrior, and a male hero as the top-paying symbol.
The Book symbol serves dual functions as both Wild and Scatter. As a Wild, it substitutes for all pay symbols to complete winning combinations. As a Scatter, three or more Books trigger the free spins feature, though notably without the scatter win payment common in many competing slots. This omission reduces the immediate value of scatter appearances but maintains focus on the feature trigger itself.
Book of 99 differentiates itself through a persistent collection mechanic displayed via a meter on the left side of the game interface. Every Book symbol that lands during base game play increments this counter, regardless of whether it contributes to a winning combination or scatter trigger. The meter tracks progress toward 99 collected Books, at which point it automatically triggers the free spins bonus.
This system provides two distinct paths to the feature: the traditional method of landing three or more scatters in a single spin, or the cumulative approach of collecting 99 Books over extended play. The collection counter persists across sessions for individual players, creating a guaranteed progression toward the bonus that reduces the variance of feature frequency compared to scatter-only triggers.
The Wild Collection mechanic fundamentally alters the risk profile of extended sessions. Players can calculate approximate spins required to reach 99 collections based on Book symbol frequency, providing a predictable timeline for feature access. This reduces the possibility of extremely long dry spells between bonuses, a common frustration in high-volatility slots relying solely on scatter triggers.
When the collection meter triggers the bonus, the game calculates an average bet size from all spins that contributed to the 99-symbol total. The free spins then play at this averaged stake rather than the current bet level, which can benefit players who increased their wager during the collection period or disadvantage those who reduced stakes near the trigger point.
Upon triggering through either three or more scatters or completing the Wild Collection meter, players receive 10 free spins. Before the feature begins, the game randomly selects one pay symbol (excluding the Book itself) to serve as the special expanding symbol throughout the entire bonus round. This selection occurs through an animated book-opening sequence that cycles through the paytable before stopping on the chosen symbol.
During free spins, winning combinations pay normally first. After standard wins are awarded, any instances of the special expanding symbol on the reels expand vertically to fill all three positions on their respective reels. These expanded symbols then pay on an all-ways basis rather than requiring payline alignment, significantly increasing win potential when multiple reels contain the special symbol.
Book of 99 operates on a traditional 5x3 grid with 10 fixed paylines, requiring matching symbols from left to right on adjacent reels. The game features a betting range from 0.10 to 100 credits, accommodating both casual players and high rollers. The Wild Collection system tracks every Book symbol that lands, filling a meter displayed on the left pillar of the temple backdrop.
The mathematical model prioritizes consistent returns through its 99% RTP configuration, balanced against high volatility that creates potential for significant individual wins. Symbol values range from low-paying royals requiring three-of-a-kind to premium character symbols paying from two matches, with five-of-a-kind premiums delivering 75x to 500x stake multipliers.
The pay-all-ways mechanic for expanded symbols creates exponential value scaling. A single expanded symbol on one reel pays once. Two reels with expanded symbols generate multiple combinations as each symbol position on reel one combines with each position on reel two. Three reels create 27 possible combinations (3x3x3), four reels produce 81 combinations, and five reels deliver 243 ways to win from the expanded symbols alone.
This mathematical structure makes the special symbol selection critical to feature value. Low-paying symbols expand more frequently but deliver smaller per-combination wins. High-paying symbols appear less often but generate substantial payouts when they do expand across multiple reels. The top symbol expanding across all five reels theoretically produces 243 combinations at 500x stake each, though game logic and reel design prevent such maximum outcomes from occurring with meaningful frequency.
Book of 99 carries a high volatility rating, indicating that wins occur less frequently but with larger average values compared to low or medium volatility games. The 99% RTP distributes across this volatility profile, meaning players should expect extended periods of declining balance punctuated by occasional significant wins that recover losses and generate profit.
The maximum win potential of 12,070x stake represents a strong but not exceptional ceiling for high-volatility slots. This figure becomes more impressive when contextualized against the 99% RTP, as most games offering similar maximum wins operate at 94-96% return rates. The combination suggests more frequent mid-range wins (50-200x stake) compared to competitors, with slightly reduced probability of reaching the absolute maximum payout.
High volatility combined with 99% RTP creates specific bankroll demands. Players should prepare for variance swings requiring 200-300x stake reserves for reasonable feature hit rates during typical sessions. The Wild Collection system mitigates some variance by guaranteeing feature access within a calculable timeframe, but individual free spins rounds can still produce results ranging from minimal returns to several hundred times stake.
Relax Gaming employs a comic book art style that renders Greek mythological characters with exaggerated features and bold outlines. The aesthetic choices create clear visual distinction between symbols while maintaining thematic coherence. Character designs range from heroic to unsettling, with the Lamia symbol particularly noted for its creepy appearance that contrasts with the otherwise adventure-oriented tone.
The base game presents a stone temple backdrop with architectural pillars framing the reels. The left pillar houses the Wild Collection meter with clear numerical display, while the right pillar contains game controls including quick spin toggle, bet adjustment, spin button, autoplay settings, and paytable access. This symmetrical layout provides intuitive navigation without cluttering the primary play area.
Free spins transition to a brighter environment depicting an idealized Greek landscape with warm lighting and classical architecture. This visual shift clearly demarcates feature play from base game sessions while maintaining thematic consistency. The expanding symbol animations execute smoothly, with clear visual feedback showing symbols stretching to fill reels before win calculations occur.
Audio design supports rather than dominates the experience. The base game soundtrack features steady percussion with melodic overlays that establish atmosphere without becoming repetitive during extended sessions. Feature triggers and significant wins receive appropriate audio emphasis without excessive celebration that might annoy players during long gameplay periods.
Book of 99 enters a saturated market segment dominated by Book of Dead, Legacy of Dead, Book of Shadows, and numerous other Egyptian and mythology-themed book slots. The primary differentiator remains the 99% RTP, which exceeds competitors by 2-5 percentage points. This advantage translates to approximately 2-5 additional credits returned per 100 wagered compared to standard alternatives.
The Wild Collection system provides secondary differentiation by reducing feature frequency variance. Competitors relying solely on scatter triggers can produce extremely long gaps between bonuses, while Book of 99 guarantees feature access within the collection timeframe. This appeals to players frustrated by dry spells in traditional book slots, though it may reduce the excitement of unexpected scatter hits for those who prefer pure randomness.
Book of 99 serves specific player profiles particularly well. Bonus hunters and players working through wagering requirements benefit enormously from the 99% RTP, as it minimizes expected losses during playthrough. The high return rate makes this slot among the most efficient choices for converting bonus funds to withdrawable cash, assuming the casino permits it for wagering.
Long-session players who enjoy extended gameplay rather than quick hit-and-run approaches will appreciate how the RTP sustains bankrolls through variance. The Wild Collection system provides tangible progression feedback, creating psychological engagement through visible advancement toward the guaranteed feature trigger. This suits players who find pure randomness frustrating and prefer measurable progress mechanics.
Book of 99 succeeds through mathematical optimization rather than mechanical innovation. Relax Gaming has created a competent book-style slot that executes familiar features reliably while offering unprecedented player value through its 99% RTP configuration. The Wild Collection system adds meaningful variance reduction without fundamentally altering the core gameplay loop that defines the book slot category.
The game will not satisfy players seeking novel mechanics or groundbreaking features. Its value proposition centers entirely on superior mathematics applied to proven gameplay structures. For players who enjoy book slots and prioritize long-term value over novelty, Book of 99 represents the optimal choice in its category. The 12,070x maximum win provides adequate upside potential, while the 99% RTP ensures that bankrolls sustain through the variance required to pursue it.
Relax Gaming has demonstrated that innovation in slot design need not focus exclusively on feature complexity. By addressing player concerns about declining industry RTP standards, Book of 99 offers a refreshing alternative that respects player value while delivering solid entertainment within established genre conventions.
Book of 99 offers a 99% RTP, which is exceptionally rare in the online slot industry where most games range from 94-96%. This means the game theoretically returns 99 cents of every dollar wagered over the long term, providing significantly better value than competitors and making it ideal for extended play sessions and bonus wagering.
Every Book symbol that lands on the reels is collected in a meter, regardless of whether it forms a winning combination. Once you collect 99 Book symbols, the free spins feature automatically triggers. This provides a guaranteed path to the bonus alongside the traditional method of landing three or more scatter symbols in a single spin.
Yes, Book of 99 offers two distinct trigger methods. You can activate the 10 free spins either by landing three or more Book scatter symbols in a single spin, or by collecting 99 Book symbols through the Wild Collection meter over multiple spins. Both methods award the same free spins feature with expanding symbols.
The maximum win in Book of 99 is 12,070x your stake, which translates to 1,207,000 credits when playing at the maximum bet of 100 credits. This potential is achieved through the free spins feature when the expanding special symbol covers multiple reels and pays on all-ways basis rather than fixed paylines.
Book of 99 is classified as high volatility, meaning wins occur less frequently but tend to be larger when they hit. Players should maintain a bankroll of at least 200-300x their chosen stake to weather variance swings. The 99% RTP helps sustain bankrolls during dry spells better than lower RTP alternatives.
When the Wild Collection meter reaches 99 symbols and triggers free spins, the game calculates an average bet size from all the spins that contributed to the collection. The free spins then play at this averaged stake amount rather than your current bet level, which can benefit or disadvantage you depending on bet adjustments during collection.
The top-paying hero symbol offers the highest win potential when selected as the expanding symbol, paying 500x stake for five-of-a-kind. However, lower-paying symbols appear more frequently and can still generate substantial wins when expanding across multiple reels due to the pay-all-ways mechanic that creates up to 243 combinations on five reels.
Yes, Book of 99 is excellent for bonus wagering due to its 99% RTP, which minimizes expected losses during playthrough. However, always verify that your casino permits this slot for bonus wagering, as some operators exclude high-RTP games from bonus play or apply reduced contribution percentages to protect against bonus abuse.
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