So your players have gone into a casino and want to gamble? Here are a few basic systems for some common games. These are mostly tuned for D20, but should work for other game systems with minimal adjusting.

Roulette

An American-style roulette wheel has 38 numbers, so the odds are pretty easy to simulate with a d20 roll (rerolling 1s). In this system, players don’t really specify exactly what they bet (it’s not a pure simulation), just the odds they’re going for. Payout indicates how much they’ll win times what they bid (e.g., a Single Number returns 36 gp if the bet was 1 gp).

If multiple PCs are playing at once, assume they coordinate their betting (e.g., if one player is betting Column, and another bets Single Number, assume the first player bet the same column that contained the second player’s single number); this way, high numbers are good for all players.

Payout Table

Bet	Payout	Roll
Single Number	36	20*
Split	18	20
Street	12	19-20*
Corner	9	19-20
Green Corner	7	18-20*
Line	6	18-20
Column	3	15-20
Red/Black, Odd/Even, or 18 Numbers	2	11-20

Using Powers and Skills

• Lucky: Players with luck that lets them periodically reroll a die can just reroll and take the better result. If the game features some kind of always-on minor luck, treating all results as one higher (up to a max of 20) is probably fair, depending on how reliable the character’s luck is.
• Telekinesis: If the player has some kind of invisible way to influence the fall of the ball in the wheel, you may call for some kind of reaction check to do it fast enough to get a useful result. The player can provide an arbitrary bonus to the roll, but for anything higher than a +1, nearby staff members get a perception check to notice that the ball is behaving oddly. If multiple players at the table are also trying to influence it, there might be a contested roll as invisible forces fight over control of the ball.
• Precognition: Depending on the strength and accuracy of precognition, the character can generally just make as much money as they want at roulette. In general, if a precog plays conservatively (mostly making 2:1 bets and losing slightly less often than they win) the cheating may only be discovered over long amounts of time. However, if the precog cannot get a constant feed of the future easily, they may have to make larger bets, and the staff will likely be very interested in looking into someone that suddenly bets big on a high-payout result after previously-normal play (leading to contested social and perception rolls).
• Telepathy: Mind reading is not helpful. The croupier doesn’t know the result any more than the players do. Mental control might get the croupier to miscall a number or mispay a bet, but this is likely to be immediately obvious to anyone else paying attention. There are safer ways to use mind-control to get money.

Slots

Slot machines have large payouts with commensurately small chances. Assume that a relatively-fair slot machine will be set up with about a 96-97% payout rate: for every 100 coins deposited in the machine, the machine returns 96 or 97, and keeps 2 or 3.

This payout isn’t usually as simple as 1/100 spins pays the full money, and the rest lose. Some may be mega-payouts that ultimately pay out less than 1/100 times, but pay a lot when they do hit. Others may be designed for variable reinforcement, paying out much more frequently for smaller amounts. Two basic systems for the two types are below.

Jackpot Slots

The player rolls one or more d20s, depending on the size of the jackpot. Only with all dice showing 20 does the machine hit the jackpot and pay out the listed amount. The jackpot is a multiple of the cost of the payment to play (e.g., a 19 jackpot for a cp coin slot returns 19 cp).

d20s	Jackpot
1	19
2	388
3	7,760
4	155,200
5	3,104,000

Variable Reinforcement Slots

This slot machine pays out more often, but pays out less. Roll a d20 for each play, and the machine pays out based on the roll (e.g., on a 19, which pays out 4, one coin was put into the machine and four came back out). On a roll of 20, roll another d20 and compare to the jackpot lines.

Roll	Payout
1-16	0
17	2
18	3
19	4
20	Jackpot
Jackpot + 1-14	5
Jackpot + 15-17	10
Jackpot + 18-19	30
Jackpot + 20	50

Using Powers and Skills

• Lucky: For luck that allows rerolling a die, it works normally on slot machines (choose which of the dice to reroll). For smaller, more consistent luck, treat rolls as one higher (and may require some kind of roll to activate). In general, this latter type of luck shifts the payout so the character can consistently make +50% over a long play session (e.g., after spending 300 coins on the slots, the character will have 450 coins). On average, it takes about six seconds to put in a coin and get a result on a standard slot machine (hey, a round!), so an attentive slot player can put in 600 coins in an hour, getting back 900 with this more consistent kind of luck. The staff are likely to notice if this continues for quite some time, but likely won’t question it for the first hour or two.
• Precognition: Seeing the future has very little effect on a standard one-coin slot machine: assume the inner-workings aren’t truly random enough that a precog can time the pull of the lever to generate a better result. If the precog has access to several of them, however, they can identify the one most likely to pay out at a given moment. Make whatever rolls are necessary to activate the power, then preroll for each of the machines, tell the precog the result, and let them play the ones with the better payout. This is not likely to make much difference in the short run (since once that machine is used, it rerolls normally for the next pull), but might if the precog can wander past a row of slots every so often after others have used them. As usual for cheating, the staff will eventually notice someone wandering the aisles, only playing slot machines that are ready to pay out.

Blackjack

Blackjack tends to have a much smaller house edge than roulette or slots, giving a standard player with basic understanding of the game and no special powers a basically-even chance of winning or losing money over time. A conservative player that comes to the table with 1000 coins, on average, will walk away with 997-999.

For standard play, simply ask the player how much they’re coming to the table to bid for a session. Assume a normal session is at least a hour of play, and the table bet maximum may influence how much a player could reasonable play at a table (a character looking to play with 1000 gp over an hour probably can’t play at the table with a silver piece per round betting limit).

Roll 2d20, add them together, and compare the result to the following chart. The payout is the percentage of the character’s starting money (e.g., on a roll of 21, the player basically came out even, taking away as much as they came to bet, though there may have been some ups and downs during the session, and on a roll of 23 a character that walked up ready to drop 10 gp walks away with 11 gp).

Payout Table

Roll	Payout
2-12	0%
13-14	20%
15-16	40%
17-18	60%
19-20	80%
21	100%
22-24	110%
25-28	140%
29-31	180%
32-34	210%
35-37	250%
38-39	350%
40	750%

Using Powers and Skills

• Gambling Skill: Unlike the previous games, skill can have a reasonably large effect at blackjack. A character that has no idea how to play might make bad bets and lose more often. Meanwhile, a skilled character that’s learned how to count cards can turn the house edge to a mild edge for themselves. Make an intelligence-based gambling skill check, with the difficulty based on how complicated the house’s shuffling system is (low for a single deck, increasing to high difficulty for multiple decks mixed together and various rules for reshuffling). A significant failure against the difficulty may impose a -1 to the final total of 2d20. A success adds +1. Major success may add +2 or +3, at the GM’s discretion. Casinos tend to be on the lookout for card counters that win big over time, banning them from continuing to play.
• Lucky: For luck that allows rerolling a die, it works normally on the result of blackjack (chose which of the dice to reroll). For smaller, more consistent luck, treat the result as one higher (and may require some kind of roll to activate). Both of these stack with gambling skill.
• Precognition: Usually blackjack is played over so many hands, with enough of a table limit, that limited-use precognition is not very helpful: if you can only see the future a few times a day, you’re just as likely to see a hand where the dealer wins as one where you do. Table limits to bets likely keep this from making a difference (and it might be very suspicious to only bet the table limit a couple of times when you barely beat the dealer). Treat the result of this as a +1 for every use of precognition for the session. Meanwhile, always-on precognition, as with roulette, can let you win as much as you want from blackjack, and the trick is to keep from getting caught. Add as big a number as you’d like to the die result, but the bigger the number, the more suspicious the staff will be.
• Telepathy: As with roulette, there isn’t a lot of hidden information for mind reading to find, and mind control to mess up the dealer is likely to be noticed by all the eyes on the table.

Poker

Alone among the games in this list, poker isn’t played against the casino, and is purely about the skill and luck of the players. Generally, the house either takes nothing from poker (though in this case many suspect some consistent players are working for the house) or takes a small rake from the table or amount of the tournament pot. But, unlike the other games, you don’t stand to win functionally-unlimited house money if you’re really lucky: if you’re playing poker against three other people, a win just gets you the money the other players are willing to put into the pot.

Basic Game

At the beginning of the game, each gambler puts in the standard amount of the table for chips (e.g., at a 10 gp table, it costs 10 gp to play).

Each gambler at the table makes a gambling skill check representing several rounds of play (taking several minutes for each round). The gambler that rolls lowest goes bust. Distribute their current chips evenly around the table, with the remainder going to the highest roll. That player might be able to buy back in at the table cost to keep playing.

Repeat this roll for each round, slowly eliminating players until there is only one left. If the table allows it, a gambler may exit with their current value in chips before rolling for a round, rather than risking going bust.

For example, a 10 gp table has four players. After the first round, one player goes bust and the remaining players now have 13 gp, 13 gp, and 14 gp, but the bust player buys back in for 10 gp. After the second round, one of the 13 gp players goes bust (split 4 gp, 4 gp, and 5 gp), leaving totals of 14 gp, 17 gp, and 19 gp (the same player rolled highest both rounds). At this point, the player with 17 gp exits while still ahead. After the final round, the winner walks away with 14 + 19 gp (33 gp).

Tournament Play

Tournaments generally take a buy-in at the beginning, do not let players that go bust buy back in, and do not let players walk away while they’re ahead. Each match of the tournament is basically a table of gamblers trying to eliminate all but one, who moves on to the next round. Obviously, different tournaments might change some of these rules, but they simplify play overall.

Essentially, iterate multiple basic games, with the player characters only moving on if they win their tables. As a hedge against one bad roll making you go bust even though you handily won previous rounds (and thus should have a big chip advantage), you might choose to give the winner of each round a cumulative +1 for subsequent rounds at the same table.

Gradually increase the skill of the opponents at the table as the player characters approach the final match of the tournament.

If they are eliminated early, players may receive a prize for previous table wins. For simplicity, assume they recoup their tournament entry fee for winning each match (e.g., 4x their entry fee for being eliminated in match 5). The overall winner of the tournament instead gets half the total entry fees. (You can do more exact math if you want; this is a quick and dirty way to split it up.)

Using Powers and Skills

• Gambling Skill: Gambling skill is key to the whole operation, and already built into the basic rules. Note that players might choose to configure exactly how their skill manifests, based on whether they’re bluffing, purely playing the odds based on visible cards, or trying to catch other people bluffing (i.e., for D&D 5e, player’s choice of using Charisma, Intelligence, or Wisdom as the attribute involved in the Cards tool roll).
• Skill-based Cheating: Sleight-of-hand is the traditional way to cheat at cards. The type of game might make this harder or easier to do (e.g., it’s pretty hard to do for televised Texas Hold’em, but might be fairly easy in a dimly-lit pirate bar playing stud). Each round of a match, make a contested check against the non-allied onlooker with the highest perception, on success gain a bonus to the round’s gambling roll, and on a major failure you’re caught. (For 5e, roll Dexterity (Sleight of Hand) against the highest Passive Perception of anyone that might turn you in for cheating. On success, gain Advantage on your gambling roll, but if you fail by 5 or more, you’re caught cheating.)
• Lucky: For luck that allows rerolling a die, it works normally on the gambling check each round. For smaller, more consistent luck, gain a +1 or the equivalent to your gambling rolls.
• Precognition: Poker is iterated over enough hands, that a single glimpse of the future usually won’t completely swing the match, but can reveal whether you’ll win a high-value hand or should avoid going bust trying to match the player with the better result. Treat a limited use of precognition as Skill-Based Cheating or Lucky, letting you reroll a round and take the better result. If you have always-on precognition, act as if you’re doing Skill-Based Cheating on every round (there’s still some luck involved in the cards you get), and prepare to make social checks to prevent others from realizing how easy it is to win.
• Telepathy/Clairvoyance: The ability to know what cards another player has is massive, either by reading their mind or viewing their cards. Similarly, mind control can fairly-subtly convince a player to bet big on your high hands or fail to push you when they’ve got a winning hand. Essentially, if you’ve successfully used telepathy on another gambler at the table, you can cause them to automatically go bust instead of the actual loser after the rolls are revealed for the round; you generally want to wait to use this until you’d go bust if they didn’t.