Book of Cthulhu Slot by KA Gaming

The reels sit inside a waterlogged abyssal temple, with two stone columns wrapped in writhing teal tentacles holding up the grid. A colossal silhouetted Cthulhu spreads its curls across the top of the screen, and carved eye sigils on the columns blink in cyan. Royals drip down in cyan, green, and red paint; the higher symbols are a purple-robed High Priest, a grey octopus-faced Cthulhu with red eyes, a single purple Beholder eye, and a horned buffalo skull. KA Gaming usually leans cartoonish, but the art here plays the Lovecraft horror angle straight.

Mechanically this is the Book-of-X formula, dressed in tentacles. The Book itself is the shipwreck illustration with "WILD" stamped beneath it, and it does triple duty: it substitutes for every other symbol, it scatters from anywhere on the reels, and it pays its own line wins, with five across one of the 20 lines worth 1000x the line bet. Top symbols pay from two of a kind, which is the Book-of-X tell that makes the base game feel a bit denser than a normal 5x3.

Three, four, or five Books trigger 10, 15, or 25 free spins. Before the round starts, the game picks one symbol at random from the regular paytable (anything except the Book) and tags it as the expanding symbol for the entire round. That choice locks in, so the run lives or dies on which symbol got picked. The High Priest at 500x for five is the dream pull; the 10 royal at 50x is the heartbreak.

Each free spin resolves twice. First the game pays any normal left-to-right line wins. Then, if the chosen symbol appears anywhere on the reels, it expands to cover the full reel, and the expansion only triggers when it actually pays something. The expanded version ignores adjacency and pays across all 20 lines at once, which is how full-reel coverage on a high symbol stacks into the 5,000x ceiling. Retriggers are baked in too, the free-game reel strip clusters Books in triples around the same stop, so a second round on top of a hot symbol is the realistic ceiling chase.

No buy bonus, no ante, no jackpots, no tumble. The whole game is the expanding symbol gamble, and that's the deal you're taking when you sit down with this one.