Evoplay released The Castle of Slotenstein on October 15, introducing a Frankenstein-inspired online slot built around a three-booster Hold & Win bonus and a Grand Reel of Fortune finale.
The game takes place in a fictional mad scientist’s castle, where players encounter a towering monster and three coloured pumpkin Bonus symbols that determine which boosters become available during the bonus round. The launch continues Evoplay’s use of seasonal themes alongside layered bonus mechanics, following earlier releases built around similar systems during 2026.
The Castle of Slotenstein uses three boosters, named Shock, Trick and Treat, to influence the development of its bonus feature. Players can activate the boosters through the corresponding coloured Bonus symbols in the main game, with the available combination determining how the Hold & Win round begins.
‘The Castle of Slotenstein gives the classic Frankenstein story an Evoplay twist, combining a spooky Halloween setting with a feature set designed to keep the action building. The three boosters each change the way the Bonus Game develops, while the Grand Reel of Fortune gives players a target to chase as they work through the feature,” Ivan Kravchuk, CEO at Evoplay, said according to European Gaming News.
Three Boosters Shape the Hold & Win Feature
The slot’s main game introduces the symbols that determine the bonus round’s starting conditions. Green, purple and blue pumpkin Bonus symbols correspond to Shock, Trick and Treat, respectively. Depending on which symbols appear during the triggering spin, the Bonus Game can begin with one, two or all three boosters active.
The Green Shock booster increases the initial number of bonus spins from three to four. This provides an additional spin at the start of the feature.
Purple Trick changes how Bonus symbols appear and interact with one another. During the bonus round, the booster allows Purple Bonus symbols to fill empty positions on their reel and increase the values of existing Orange Bonus symbols on that reel. Purple Bonus symbols can carry values ranging from 0.5x to 5x the player’s bet.
The Blue Treat booster also introduces additional value to the bonus round. Blue Bonus symbols carry values from 0.5x to 5x the bet, which are added to every Orange Bonus symbol on the game field when the booster is active.
Orange Bonus symbols appear exclusively during the Bonus Game and award random values ranging from 0.5x to 5x the bet. Only Bonus symbols appear on the reels during this feature, and each newly landed Bonus symbol resets the remaining spin counter. This mechanism allows the round to continue as new symbols arrive, creating further opportunities to fill individual reels.
The game also includes a Wild symbol in the main game. It substitutes for regular symbols in winning combinations, excluding Bonus symbols, and appears only on reels two through five.
Grand Reel of Fortune Adds a Final Prize Round
The central progression mechanic comes into play when players fill a reel with three Bonus symbols. Once all three positions on a reel contain Bonus symbols, the game collects their displayed values and adds them to the win meter. The completed reel is then cleared, making its positions available for subsequent Bonus symbols.
The first time each reel is completed during the Bonus Game, the corresponding section of the Grand Reel of Fortune becomes unlocked. The feature contains five sections, and players must unlock all of them to activate the final prize round.
After all five sections have been unlocked, the game awards one final spin on the Grand Reel of Fortune at the end of the Bonus Game. The wheel can produce one of eight outcomes: multipliers of 2x, 3x, 5x or 8x, or one of four fixed prize categories named Mini, Mega, Super and Grand.
The Grand Reel of Fortune is available only during the Bonus Game, linking its final spin to progress made on the reels. Completing each reel for the first time contributes to unlocking the wheel, while the collected Bonus symbol values feed into the win meter.
This structure gives the feature two connected elements: collecting values from completed reels and unlocking the sections required to reach the final prize spin.
Bonus Buy Offers Direct Entry
The Castle of Slotenstein also includes a Bonus Buy option, allowing players to purchase immediate access to the Bonus Game rather than waiting for the feature to trigger through regular play.
The option provides a choice of entering with one, two or all three boosters active. This lets players select the starting configuration for the bonus round, including combinations that activate Shock, Trick and Treat together.
Evoplay has used booster mechanics in other releases during 2026, including 3 Super Volcanoes and Tiger of Fortune, as well as titles associated with Oktoberfest and Asian mythology. The new Halloween game applies a similar approach to a monster-themed setting, with the coloured pumpkins serving as the link between the main game and the bonus feature.
The online slot‘s action takes place on a grid with 5 reels and 3 rows, featuring 20 paylines. According to the developer, the title is built using HTML5 technology and supports Full HD resolution in a 16:9 format. It has a stated return to player (RTP) of 96.20% and low volatility.
The release adds another seasonal title to Evoplay’s portfolio, with the Frankenstein setting providing the backdrop for a bonus system based on coloured symbols, reel completion and a final wheel-based prize.