Coins of Poseidon 2

Hold and Respin, or 'Hold & Win', is one of the most popular core bonus game mechanics in modern slots. The essence of this feature, unlike traditional free spins, is to 'Hold' bonus symbols on the reels and 'Respin' the remaining empty spaces to fill up the screen. This system was popularized worldwide through 'Money Train 2's' 'Money Cart Bonus' and is the foundation for numerous developer-specific brand features like Wazdan's 'Hold the Jackpot™' and Playtech's 'Fire Blaze™'.

A Feature Upgrade is a very special 'meta' feature that, rather than paying out winnings itself or directly affecting other symbols, enhances another special feature symbol (e.g., Collector, Payer) already on the reels to a more powerful 'Persistent' version. The core of this feature is to change the 'nature' of other special symbols that determine the potential of the bonus round, instantly transforming what could have been an average bonus into a round where one can expect the Max Win.