A look at Stacked Symbol Slot Machines

By John Grochowski
Video slots are the most popular, most played and most widely available games in modern casinos. They’re also the games with the most variation, full of little wrinkles that affect game play.
One of those wrinkles introduced in recent years has been the use of stacked symbols. When symbols are stacked, a reel can show three of the same symbol, from top to bottom. That symbol this is part of the mix on all paylines.
The effect is to add volatility to the game, which was apparent in a session I played while my wife was elsewhere in the casino searching for old favorites.
I came across an area where machines are marked as new games, and went try one I’d never played before, IGT’s Cherry Mischief. It was a 40-line penny game, so I was wagering 40 cents a spin. All symbols were sometimes stacked in the IGT Super Stacks feature. Among the symbols were young women with fairy wings, and a butterfly symbol that if stacked on reels 2, 3 and 4 launched a free games feature.
I slid a $20 bill into the validator, and quickly ran into the downside of stacked symbols. Symbols in a stack can block potential winning combinations, as when blonde fairies on reels 1 and 2 were separated from the match on reel 4 by a stack of red-headed fairies on reel 3.
That happened fairly often. The good news: I was seeing stacked symbols frequently on all reels, giving me hope that at some point, I’d see stacks of like symbols on adjacent reels starting from the left. That could give me a big multi-line win. The bad news: The stacks were interrupting sequences that could bring small wins to extend my bankroll and keep me at the machine.
Before long, my 2,000 credits were down to 85. I had to face the possibility that I might run through my $20 without ever really seeing what the game could do.
But my luck turned. The “Q” for “Queen” symbols stacked on all five reels, a screenful of Qs for a 520-credit win. It wasn’t an enormous win, but large enough that I had a little room to work, some extra spins to see if something bigger would come a long.
A few spins later, it happened. Reel No. 2: Three stacked butterflies. Reel No. 3: Three stacked butterflies: Reel No. 4: Three stacked butterflies. I was going to the free spins bonus event.
On free spins bonuses, there is never any guarantee of wins. You can come out of 15 free spins with thousands of credits, or with barely enough for another minimum-coins spins. My first few freebies, it was looking like the latter. Three 10 symbols in a row here, three Aces there, but nothing big. After four spins, my bonus stood at 60 credits.
Then a couple of good spins made my round. Three dark-haired fairies stacked on the first three reels for an all-payline win, and there was one matching symbol on the fourth reel to enhance the payback. Next, three golden-haired winged lovelies stacked on the first three reels for another all-line win.
The free spins put 1,860 credits on my meter, briefly putting me into the profit zone by a couple of dollars. I played down to my original $20 and moved on.
When you play stacked symbol games, that’s the kind of experience you expect. There will be fast losses, and there’s a fair chance of big all-line wins. You’re just hoping the balance falls in your favor.

A WORD ABOUT VOLATILITY: Stacked symbols are one of the tools game designers use to put volatility into video slots. When the video games first rose to popularity in the late 1990s, most were nickel games, and most had pick’em-style second-screen bonus events. Part of their attraction was that they were less volatile than three-reel slots, where it was possible to go a couple of dozen spins without winning anything. The pick’em games were designed to extend the playing experience and keep people in their seats with frequent small wins.
When penny games started to take over casino floors, designers had to find a way to give players meaningful wins. A 200-credit pick’em bonus was a nice $10 win on a nickel game, but with pennies it’s only 2 bucks.
 Free-spin games, where the bonuses can be next to nothing but also can be thousands of credits, already had been pioneered by Australia’s Aristocrat Technologies. Other manufacturers put their own spin on the format, and the majority of penny games today are free-spin games. Pick’em bonuses are still there, and so are hybrid games with both kinds of events, but playing for pennies largely means playing for free spins.

John Grochowski writes a weekly syndicated newspaper column on gambling, and is author of the "Casino Answer Book" series from Bonus Books.