Book of Cthulhu is a five-reel video slot from KA Gaming, set among sunken ruins and ancient creatures. Its 20 paylines give the base game a familiar shape, while Book Scatters lead to Free Games with a reel-filling symbol feature.
Quick take: A Lovecraftian line slot where a qualifying winning symbol can expand across its reel during Free Games.
Theme and Gameplay
The sunken-ruin setting gives the familiar line game a horror backdrop. On ordinary spins, the five reels and 20 paylines keep the task clear: follow the symbols along the lines, then watch for Book Scatters that can open the feature. Matching symbols need to form a paying line combination; their presence elsewhere on the reels is a separate matter.
The contrast between the regular line game and the expanding symbol gives the bonus its main visual change. Once Free Games begin, the selected symbol becomes the one to follow closely.
Slot Features
Book symbols act as Scatters and trigger 10 Free Games. Before the feature begins, one symbol is randomly selected to expand. When enough of that symbol land to make a win, it fills its reel vertically and can pay across all 20 lines.
That makes the chosen symbol worth tracking alongside the Scatter books. The books open the round, while the selected symbol supplies its distinctive winning effect. A single appearance does not automatically mean an expansion: enough copies must land to form a qualifying win first.
Feature focus: In Free Games, watch which symbol was selected and whether enough copies land to form a win; that is when it expands to fill its reel.
RTP and Win Potential
The game has a 96.5% RTP, medium volatility and a 526x maximum win. RTP describes a long-term theoretical return, rather than what a short session will pay. The ceiling is relatively modest for a feature-led slot, and the expanding symbol still needs a qualifying result before it can broaden a win across the paylines.
My Thoughts On This Slot
The expanding-symbol feature gives the Free Games a clear purpose: a winning symbol can take over a full reel and reach every payline. That is an easy change to understand, and it makes the selected symbol more interesting to follow than a standard free-spin counter alone.
The appeal is focused, which suits someone who wants a straightforward line game with a distinct bonus idea. Anyone primarily chasing very large top wins may find the ceiling less appealing, but the Lovecraftian setting and conditional reel expansion give Book of Cthulhu a specific hook.
Final Take: A focused horror slot whose selected symbol gives the Free Games a clear target to watch.
