Book of 99 Slot 

Relax Gaming are the team responsible for the Book of 99 slot, a May 2025 release that leans heavily into the fabled mythos of Ancient Greece. Featuring gods and creatures such as Apollo, Pythia, and a cyclops, the imagery in this release really stands out from other online slot games in the developer’s library. The unique nature is exemplified further when taking into consideration the bonuses this Book of 99 slot comes with, too, as there are additional expanding symbols and progressive trail mechanics that have been included.

Before getting into any of the nuanced elements in the Book of 99 slot, though, it is important to first break down the gameplay blueprint it presents to players. Sitting in the middle of the screen and backed by weathered stone segments are 5 reels and 3 rows, which feature 10 payline paths spread across them. Directly above this playgrid is the golden Book of 99 logo, and off to its left, a progressive trail decorated with Greek mosaics can be seen.

The entire frame that surrounds the Book of 99 playtable is designed like a classic Greek temple, featuring thick pillars on either side of the reels. Looking at the backdrop, a coastal landscape fills the screen, with cliff faces plunging into the ocean's water below. A couple of caves can be seen amongst the stone cliffs, each of which is topped by tall green trees. By focusing on nature as opposed to mythical cities, the Book of 99 slot presents an aesthetic that remains distinct compared to other genre entrants like Gates of Olympus and Wisdom of Athena.

Carved out of stone and backed by different coloured mosaic patterns, the lower-valued symbols in the Book of 99 slot are 5 different card royals, like those seen in live casino games. As for the higher-valued portion of the paytable, this features a series of Greek gods and creatures that are deeply embedded in this civilisation's mythos. 

Lower Value Symbols:

10

Jack (J)

Queen (Q)

King (K)

Ace (A)

Medium Value Symbols:

Lamia

Cyclops

Higher Value Symbols:

Pythia

Apollo

There is just a single bonus symbol in the Book of 99 slot, namely the titular book. This acts as both the wild and scatter symbol, having a dual role just like the bonus symbols found in the similarly-named Book of Dead.

If a book symbol is landed on any of the 5 reels of play, it can step in and assume the value of any base game symbols in the Book of 99 slot to make or increase a combination. This is all down to it acting as the wild symbol in this Greek-themed release, which means it possesses substituting abilities.

Players could potentially trigger 10 free spins in the Book of 99 slot if they happen to land 3 or more of the book symbols at the same time, as the book also steps in as the scatter symbol. Before the bonus round begins, though, a book is opened, its pages turning in an impressive animation. Randomly, the pages will come to a stop, revealing a base game symbol. If this same symbol appears during the Book of 99  free spins, this may expand and fill a full reel of 3 rows, just like the modifier found in Legacy of Dead. Should the bonus round be retriggered, the book animation will play out again before selecting another random base game symbol.

During play, if any book wilds are landed on the playgrid, these are actually collected by the mosaic-pattern ladder off to the left of the reels. If 99 books are added to this, it could potentially trigger the Book of 99 free spins round, before resetting back to 0 again.

No different from other UK online casino releases by Relax Gaming, the Book of 99 slot is fully compatible with smartphones, PCs, and tablets. By including HTML5 software, the developers have ensured that the gameplay experience and detailed graphics remain the same regardless of the device type. This is possible as long as the play method used is connected to a stable source of internet.

Overall, the Book of 99 slot manages to fuse a range of unique Greek mythology-inspired symbols with a polished base gameplay blueprint and some inventive free spin modifiers. Relax Gaming have showcased their expertise here, combining all of the unique elements together impressively. 

Titles like Book of Aztec and Book of Riches Deluxe also feature the same expanding symbol bonus mechanic if you enjoy this dynamic detail in the Book of 99 slot.

Please remember to always gamble responsibly, this is a real money gambling site.