A good deal of "cascading reels slots" turns on a handful of special symbols. Most of the excitement in a modern slot sits in its features: wild symbols that complete lines, scatters that start a round, and bonus games with free games, multipliers or prizes to pick. Each feature follows written rules about how it triggers and what it can award. Reading those rules shows where a game keeps its biggest moments and how often a player should expect to meet them.
A wild symbol stands in for other symbols to complete a winning combination, usually with the exception of scatters and bonus symbols. Many games add a twist: wilds that expand to fill a whole reel, stay in place for several spins, move across the grid or carry a multiplier. The paytable shows which version a game uses and whether a line completed by a wild pays at the normal rate or at a raised one.
Cascading reels remove winning symbols after a payout and drop new ones into the gaps, so one spin can produce a chain of wins. Games with cascades often raise a multiplier with each step of the chain and reset it when the chain ends. Respin features work in a similar way, locking special symbols in place while the other positions spin again. The feature rules explain when each chain or respin comes to an end.
A wild replaces most other symbols to finish a winning combination, though scatters and bonus symbols are usually excluded; the paytable says whether wild wins pay a boosted rate.
Winning symbols vanish after each payout and new ones drop into the gaps, and the chain stops once a fresh drop forms no further winning combination.
Some wilds carry a multiplier that boosts any line they complete, while cascade games often raise a multiplier with each step of a chain and reset it afterwards.
Every slot publishes a feature rules page covering triggers, awards, retrigger limits and prize ranges, and one read explains what a quiet run of base game spins means.