Serial review
Serial is a Nolimit City slot from November 2022 about the “Bodycam Butcher”, a serial killer with a camera on his chest. The theme is harsh and not to everyone’s taste. But under the grim wrapper sits one of the studio’s most carefully built maths models: respins with sticky symbols, Enhancer Cells, symbol splitting and a free 50/50 on the biggest wins.
Three rows, five reels and the pay table
Wins count by ways: a combination forms on neighbouring reels from the left, starting at the first. There are five low symbols, sinister objects. There are five highs as well: bones, a frightened woman, a bloodied “doctor”, a policeman and the Bodycam Butcher himself. For five matching symbols without modifiers the lows pay 0.5x to 0.9x the bet and the highs 1x to 5x. The Wild comes in three kinds, regular, xNudge Wild and xSplit Wild, all substituting for every paying symbol, while the scatter carries a spin count and triggers the bonus.
The biggest line payout is only five bets, so this game pays through modifiers rather than the table. That is the point of all its mechanics: they grow the ways and the multipliers.
Respins: a win stays on the grid
All winning symbols stick and the other reels spin again. Every respin that improves the win gives another. While the chain runs, the total grows. On each respin Enhancer Cells above and below the grid open from left to right, one reel at a time.
That changes the approach to the base game. A first win is not the end but the start of a run: sticky symbols reduce the number of free places and raise the chance of completing a combination, and every opened cell brings new symbols.
One respin chain step by step
An imagined example. The first spin brings a win of three matching symbols and they stick. The two remaining reels spin again, and on the first respin two cells open: one above the first reel and one below. The upper one holds an xNudge Wild, the lower a character symbol. The win grew, so a second respin is awarded.
On the second respin the cells above and below the second reel open. Say they hold an xWays and an ordinary Wild. The xWays reveals three symbols, its ways rise and the win grows again. Respins continue while the win grows and end on the first respin that improves nothing. That is why even a modest start should not be written off.
Enhancer Cells: what can land in a cell
On a respin two cells open, and each can show one of four things:
- xWays, which reveals 2 to 4 matching symbols and raises the number of ways;
- xNudge Wild, which nudges until fully visible, each step adding +1 to its multiplier;
- an ordinary Wild, a plain substitute;
- a character symbol, any of the high symbols.
The cells are the main source of improvement. Even a weak win can turn into a big one if an xWays on a high symbol appears in the opened cells.
xNudge Wild: steps and multiplier
This is a tall Wild that always nudges until fully visible. Each step raises the multiplier by 1. For example, an xNudge Wild that landed in a cell above a reel nudged two steps and got a 2x multiplier. If another such Wild with 3x takes part in the same combination, the multipliers add up to 5x. The combination’s payout is multiplied by that sum.
The Wild can also land on reels two to four in the ordinary way. That is a second route to a multiplier besides the cells.
xWays and the infecting xWays
An xWays symbol appears only in cells or is converted from a scatter. It reveals an ordinary paying symbol and shows 2 to 4 of them. If several xWays land, all reveal the same symbol. A special variant is Infectious xWays: the revealed symbol infects every other normal-size symbol on the 3-3-3-3-3 grid, which grow to the same size.
An ordinary xWays acts locally, while the infection spreads its effect across the grid. A symbol that once stood alone grows into a column, and its number of ways rises on every reel. Exact numbers depend on which symbols were on the grid, but the principle is clear: the infection turns an ordinary combination into a powerful one.
xSplit Wild: doubling on the last reel
The xSplit Wild is a Wild with a 2x multiplier that can land only on the last reel. It splits all symbols in its row into two. Scatters split too, and the spin count on them doubles. An xNudge Wild splits and its multiplier doubles, while an xWays symbol doubles in size.
So this symbol works as an amplifier for everything else: the more special symbols in its row, the bigger the effect.
The Search: scatters carry numbers
Three scatters trigger The Search. Each scatter shows a number, and the sum of those numbers is the number of free spins. If exactly two scatters land, they turn into xWays symbols. In the bonus extra cells open on reels 2, 3 and 4 and the grid becomes 3-5-5-5-3. The enlarged grid is what sets the bonus apart from the base game.
The rules for respins and cells stay, while the starting ways rise from 243 to 3 × 5 × 5 × 5 × 3 = 1,125, 4.6 times more, before any xWays, xSplit or infection. So even without a single modifier the bonus round is denser than the base game.
The Kill: a jumping xSplit
Three scatters plus an xSplit trigger The Kill. It also starts if an xSplit lands during The Search: the round is then upgraded and 2 spins are added. In The Kill the xSplit stays on the fifth reel as a jumping Wild until the round ends and splits the symbols in its row on every jump.
The logic of the upgrade is simple: a permanent amplifier is added to the enlarged grid of The Search. That explains the gap between the buy prices of the two bonuses.
How many spins in the bonus: an example
An imagined trigger. Three scatters land with numbers 3, 4 and 5. The sum is 12, so The Search begins with 12 free spins. If an xSplit splits the scatter carrying 5, the number becomes 10 and the sum 17. Finally, if an xSplit lands in the round itself, 2 more spins are added and the round becomes The Kill.
The ranges of numbers on scatters are not published, so the average bonus length cannot be estimated. But the example shows that the spin count floats in this game, and a bought bonus at 78x does not promise a guaranteed ten as many slots do.
xBizarre: a free 50/50 above 18,700x
The game’s cap is 74,800x, but the win achievable in the base game or the bonus is limited to 18,700x. Until a win reaches that threshold, xBizarre does not appear and the game simply pays as usual. If a win passes 18,700x, xBizarre switches on: up to three times you are offered a 50/50 choice for another 18,700x. A wrong choice takes nothing from what you have already won, so the player is not asked to make any decision about risk: it is a free attempt.
Each stage adds the same 18,700x step, not a growing one: right choices take the total to 37,400x, 56,100x and 74,800x. Assuming even odds, one such win in eight gets all the way to the cap, and the studio puts the chance of the maximum win itself at one in 12 million.
RTP: base game, bonus and three versions
By the studio’s figures, the main game returns 62.43% of stakes and the bonus 32.49%, about a third of the RTP while landing once in 243 spins. Together that is 94.92%, 1.15 points short of the total, and the studio does not explain the gap. Part of the return probably comes from xBizarre and other effects, but that is only a guess. Besides the main 96.07% version there are builds at 94.08% and 92.05%: the casino decides the version, and you can find it in the game’s help.
A payout comes on average on every 3.6th spin, and a win of 100 bets or more about once in 888 spins.
The buy menu: three modes and xBet
The Search — Price: 78x; What it gives: a bonus with the enlarged grid; Max RTP per Bigwinboard: 96.27%.
The Kill — Price: 480x; What it gives: a bonus with a jumping xSplit; Max RTP per Bigwinboard: 96.38%.
Lucky Draw — Price: 279x; What it gives: a draw between the two bonuses; Max RTP per Bigwinboard: —.
xBet — Price: +20% on the stake; What it gives: a scatter on the second reel is guaranteed; Max RTP per Bigwinboard: 96.04%.
The price rises 6.15 times from The Search to The Kill, while the maximum RTP of the bonus buy rises by only 0.11 points. The dearer purchase does not give more return per euro invested: you pay for a permanent xSplit, that is, for a different volatility with the same return and a noticeably wider spread of payouts. The price of The Search almost equals a rough estimate of the average bonus: if the 32.49% bonus share is spread over bonuses arriving once in 243 spins, one bonus is worth about 79 bets (32.49 × 243 / 100).
Lucky Draw and xBet
According to the Bigwinboard review, Lucky Draw gives The Search with a 70% chance and The Kill with 30%. With those shares the average price would be 0.7 × 78 + 0.3 × 480 = 198.6 bets, yet the draw costs 279. So either the split differs or something else is built into the price, for example a different RTP for each variant. The official text does not give those shares, so Lucky Draw is not a “discount” on The Kill but a separate mode with its own logic.
xBet adds 20% to the stake and guarantees a scatter on the second reel, while symbol payouts do not change. The mode speeds up meeting the bonus but does not guarantee it: three scatters are still needed and only one is guaranteed.
Its place in the studio’s line-up
Serial came out two months after Folsom Prison and continued the line of heavy slots with xWays and xSplit that began back with San Quentin xWays. The difference is that the grid here is tight, 5×3, and all the power is hidden in respins and cells. It is not a huge grid like the 6×6 of the studio’s later games, but a dense, disciplined mechanic in which every respin changes something: the rules fit on a single page, and the cap still sits high on the studio’s scale.
Closest to Serial is Karen Maneater, while Folsom Prison shares its era and its heavy presentation.
Serial — RTP: 96.07%; Volatility: very high; Max win: 74,800x; Release: 8 Nov 2022.
Karen Maneater — RTP: 96.00%; Volatility: very high; Max win: 17,777x; Release: 16 Aug 2022.
Folsom Prison — RTP: 96.07%; Volatility: very high; Max win: 75,000x; Release: 13 Sep 2022.
San Quentin xWays — RTP: 96.03%; Volatility: very high; Max win: 150,000x; Release: 12 Jan 2021.
