Book of 99: Slot Overview

With the slot market overflowing, studios need a real hook to get noticed—an offbeat theme, huge win potential, or genuinely fresh mechanics. Relax Gaming has largely avoided those routes here. As the name suggests, Book of 99 is another ‘book of’ style title, this time inspired by Ancient Greece. The win potential is also fairly typical for the genre. What Relax has done instead is lean into a striking RTP figure that matches the title, and pair it with a notably generous collection mechanic.

Visually, Book of 99 is pleasing overall—perhaps the base game is a touch plainer, but the bonus shifts to a bright, sunlit arcadia that’s easy on the eyes. The rest of the presentation also carries that familiar Relax vibe, with cartoon-styled symbols showing heroes and villains from mythic times. A few are genuinely unsettling (yes, the scary lady). The soundtrack fits well too, mixing a pulsing beat with a melody that gives the action an exotic edge.

This is a highly volatile slot, built on the classic ‘book of’ setup of 5 reels and 10 fixed paylines. Bets run from 10 p/c up to $/€100, and it plays smoothly across devices. The standout talking point is the RTP configuration. You don’t often see numbers this high, and Relax pushes against the usual downward drift by giving Book of 99 a hefty 99% RTP. Call it a gimmick or a marketing hook—either way, it’s an excellent value and makes Book of 99 far more appealing than many other games in the ‘book’ niche.

Wins are created from reel 1, when matching symbols land next to each other along a payline. In this Greek-themed journey, the lower end is made up of attractive 10-A symbols, while the higher-paying set includes Lamia the child-eating monster, a cyclops, and the main female and male characters. Low symbols require at least 3 for a payout, whereas premium symbols pay for 2 or more. If 5 top symbols connect, the reward comes in at 75 to 500 times their stake, which makes full screen hits especially exciting.

Book of 99: Slot Features

Anyone who enjoys book slots will know what to expect, and Book of 99 stays close to the blueprint established long ago by Book of Ra. The key mechanic is expanding symbols during free spins, though Relax Gaming spices things up with a collection system that isn’t commonly seen in this subgenre.

As usual, the book symbol is the gateway to the best action. It acts as a wild, substituting for pay symbols to help form winning lines, and it is also the scatter—landing 3 or more triggers 10 free spins but comes with no extra payout, which is slightly uncommon. Before the free spins begin, one pay symbol is randomly chosen as the special expanding symbol for the entire feature.

On every free spin, special symbols expand to fill all positions on their reel after standard wins have been paid. Expanded symbols pay-all-ways from any reel, meaning they don’t need to be adjacent or start on reel one. The main aim is to land full-screen results—the higher the chosen symbol’s value, the bigger the upside. One more detail: free spins are retriggered whenever 3 or more book symbols appear.

Finally, there’s the more unusual mechanic: a wild collection system. Each time a wild symbol lands in the base game, a collection meter at the side advances by 1 step. When the meter is completed with 99 collected wilds, it awards 10 free spins. Free spins triggered this way follow the same rules, so the expanding symbols are still the core of the feature.

Book of 99: Slot Verdict

Book slots are everywhere, but Relax’s take on this flagship style comes with a few strong reasons to pick it over the competition. The RTP is the obvious headline, putting Book of 99 among the most generous slots available. If you’re looking for a game to help grind through a wagering requirement, it’s tough to name a better candidate. Book of 99 could be an excellent option for improving your chances of getting something back in that scenario—assuming operators are willing to make it available for that purpose.

Beyond the unusually high RTP, Book of 99 stands up as a well-made ‘book of’ slot on its own merits. It looks good, and the wild collection system is a welcome bonus. It gives players an added sense of progress and rewards sticking with it. Even if landing 3 scatters at once feels like hard work, over time you’ll inevitably see 99 of them, which leads to free spins. That does raise another question: how is that RTP split between the base game and the free spins? Is the extremely high RTP ultimately beneficial, or could it be a drawback? There’s always the possibility that long base-game stretches start to feel like a slog. Part of what made Book of Dead such a hit is its well-balanced math model.

In the end, the combination of above-average RTP and a wild collection feature makes Book of 99 a smartly built, good-looking entry in the crowded ‘book’ market. Once again, it proves you don’t have to reinvent the wheel to deliver a solid slot—as long as there’s an expanding special symbol involved.