Prairie Thunder Keno

Introduction

Prairie Thunder Keno is a keno variant that offers multiplier and free spin with even bigger multipliers. It is made by Grand Vision Gaming. I first noticed the game at the DraftKings casino.

Rules

1. The game is based on conventional American keno with 80 numbers and a 20-ball draw.
2. After the player picks 3 to 10 numbers, the game shall randomly pick seven of the unchosen numbers. It will mark two of them with wolves and the other five with horseshoes.
3. The game shall then draw 20 numbers at random from 1 to 80. As in conventional keno, the player shall be paid according to how many of his chosen numbers match the 20-ball draw by the game. The pay table below shows the win for all combinations of picks and catches.
4. If both numbers marked with wolves match numbers drawn by the game, then any win shall be multiplied by 4.
5. If at least four numbers marked by horseshoes are drawn by the game, then the player shall play the free spin bonus.
6. The free spin bonus shall start with 10 free spins for catching four horseshoes and 12 for catching all five.
7. In free spins, the bet amount and numbers drawn will be the same as the initial spin that triggered the bonus.
8. In free spins, the game shall still choose five numbers, unchosen by the player, and mark them with horseshoes.
9. In free spins, instead of the game marking two numbers with wolves, it shall mark eight numbers, unchosen by the player, with mountains.
10. If a free spin results in at least three horseshoes matching the ball draw, then the player shall earn additional free spins. Three horseshoes shall earn 4 additional free spins, four horseshoes shall earn 10 additional free spins, and five horseshoes shall earn 15 additional free spins. Free spins may earn more free spins, infinitely.
11. If a free spins results in matching at least one mountain, then the player shall earn a multiplier from 2x to 4x. If the ball draw matches more than one mountain, any win shall be multiplied by the product of all multipliers. For example, the maximum multiplier would be 4*4*4*4 = 256.
12. The probability of each multipliers depend on the number of picks, and the multiplier table below.

The following table shows the base win for all combinations of picks and catches as used at the game at DraftKings.

DraftKings Pay Table

Catch Pick 3 Pick 4 Pick 5 Pick 6 Pick 7 Pick 8 Pick 9 Pick 10
0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0
2 2 1 0 0 0 0 0 0
3 16 4 3 2 1 0 0 0
4   39 10 4 3 3 2 1
5     228 25 9 6 3 3
6       525 110 34 14 7
7         1200 490 135 53
8           3000 1100 365
9             6000 2000
10               10000

The following table shows the probability of each Mountain Multiplier in free spins according to the number of picks.

Pick 2x 3x 4x
3 74% 16% 10%
4 75% 15% 10%
5 77% 13% 10%
6 77% 13% 10%
7 75% 15% 10%
8 73% 17% 10%
9 73% 17% 10%
10 75% 15% 10%

Examples

In the image above, I bet \$1, picked numbers 1 to 10 and wolves were placed on 16 and 37. I caught four of my 10 picks and both wolves. Normally, catching 4 pays 1, but I earned a 4x multiplier for catching both wolves, for a total win of \$1 * 4 = \$4.

In the image above horseshoes were placed on numbers 32, 36, 73, 77, and 79. Four of the five were hit (all except the one on 36), which triggered 10 free spins.

In the free spin above, I picked numbers 1 to 10 and caught seven of them, which normally pays 53. In free spins, the game marks four numbers with mountains, in this case 16, 47, 74, and 79. The mountain on 47 was caught, earning me a multiplier of 2x. Thus, my final win for that spin was \$1*53*4 = \$106.

Analysis

The following table shows the return to player for all number of picks, separated by the return from the base game and the bonus.

Pick Base Game Bonus Total
3 0.574002 0.354842 0.928844
4 0.579201 0.353708 0.932909
5 0.589172 0.344536 0.933708
6 0.589203 0.346076 0.935279
7 0.588032 0.347630 0.935662
8 0.591229 0.345632 0.936861
9 0.591085 0.345777 0.936862
10 0.594533 0.341735 0.936268

You can see the greatest return is on the pick-9 at 93.6862%. It is only 0.0001% less on the pick-8.

Acknowledgements

I would like to thank Grand Vision Gaming for correcting an earlier mistake in this page.