Expanding Symbols Slots

The Book of Ra Legacy

The expanding symbol mechanic works like this: at the start of a free spins round, the game selects one symbol (sometimes randomly, sometimes the player chooses). Every time that symbol appears during the bonus, it expands to fill the entire reel. If it lands on two reels simultaneously, both expand, and the game evaluates wins with those full columns of matching symbols.

The "Book of" genre was built entirely on this single mechanic. Book of Ra, Book of Dead, Book of Toro, Book of Sam - the formula barely changes between implementations. A special book symbol acts as both wild and scatter, triggers free spins, and selects the expanding symbol. The differences come down to which extra features sit on top: multipliers, additional expanding symbols chosen during retriggers, or modified grid sizes.

Which Symbol Gets Chosen Matters

The expanding symbol selection is where sessions diverge. High-paying symbols expanding across multiple reels produce the headline wins. Low-paying symbols expanding produce frequent but small returns. In games where the selection is random, the bonus round's potential is decided before the first free spin lands. Some implementations let you collect additional expanding symbols through retriggers, and that's where the ceiling opens up - three or four different symbols all expanding creates combinations the base paytable wasn't designed for.

Banquet of Dead from Play'n GO and Book of Arcane 100 (with its 100,000x ceiling) show the range. Same core mechanic, wildly different risk profiles built on top.