KMS Letter From Director Won-ki About MapleStory’s Probability Systems

Discussion in 'KMS Updates' started by Orange Mushroom, Feb 19, 2021.

  1. Orange Mushroom

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    The director of KMS, Kang Won-ki has posted a notice on the official MapleStory homepage addressing a new controversy related to the change in additional options rates in the test server update yesterday.

    Since many users previously thought there was something weird about certain lines appearing together, they mentioned it to Nexon who previously said the system was working as intended. However, this was revealed to be incorrect given the changes made yesterday. This letter was made in response to that and provides detailed information about some of the probability systems in MapleStory.

    Hello, this is MapleStory’s Director Kang Won-ki.

    First of all, we would like to apologize for the concern caused by the improvement of additional options which was revealed through the test server update on February 18. We had to take some time to organize the correct information. We apologize for not being able to provide guidance quicker.

    Additional Options System Change Goal and the ‘Problem where Jump and % All Stats Appear Together Frequently’ Confirmed Information

    In the process of reviewing to lower the hurdles of additional options, we determined that the weighting method for both ‘type’ and ‘tier’ of additional options was overly complex, and we decided to change the ‘type’ to have equal probability while maintaining the weighted probability for ‘tier’. Therefore, we modified the logic based on our newly developed uniform distribution rather than the logic based on different weights which was developed when additional options were introduced, and applied it to the test world update on February 18.

    After the test world update, we received a report stating that “Jump and % all stats additional options appeared together a lot, but after this patch the issue has been resolved”. Since this was unrelated to the content that we changed, we analyzed the past logic again and confirmed the parts which we misunderstood.

    For a more accurate explanation, the past additional options ‘type’ selection logic and options arrangement order will be disclosed as follows.

    1. Select the first option according to the weighted probability among the list of additional options arranged in a predetermined order.
    2. Based on the location of the selected option, separate the list into upper and lower sections.
    3. Select one option from each of the sections, according to the weighted probability.
    4. Select one of the two options with a uniform proability, and set it as the second option.
    5. Select the third and fourth options in the same way.


    In relation to this, due to the 4th final selection logic based on the first selected option, there was a high chance for certain options to appear together. For example, if damage % was chosen on a weapon or jump was chosen on armor, all stat % was alone in the lower section, so they appeared together at a high chance. However, we mistakenly thought that the related logic was ‘selecting the remaining options based on the weighted probability except for any that were already chosen’. It is our fault for not accurately understanding this issue. We apologize for any concern that we caused.

    In addition, as a result of a thorough investigation of all the probability systems that currently exist in the game, this problem is also present in the Ability system. In the case of Abilities, there is no problem when resetting tiers but the same issue has been confirmed when resetting lines. This will be modified in the official server update in February.

    Through this additional option reorganization, the problem of certain options appearing with a higher chance which many users did not understand has definitely been fixed. Going forward, if there is a questionable problem, we will actively identify the cause and correct it. Apart from this, changing all types of additional options to have the same probability is intended to slightly lower the difficulty of additional options and will be maintained. In order to accurately understand the difficulty of additional options, we will also disclose the probability of additional option tier settings.


    We apologize once again for the disappointment caused by not sharing our intentions or enough background information when making many changes to an existing system and by not properly confirming exact specs during our change process.

    The Meaning of the Word ‘Random’ In-Game

    From the beginning of MapleStory’s service, the word random has been used in-game as a collective term for ‘the act of determining a result by generating a random number according to set conditions’. Therefore, when describing probability type items or systems which determine results with fixed weights, the word ‘random’ was used. In addition to additional options, most of the probability type items and systems in-game have the same description.

    After this, we will check all of the probability type items and systems in-game and modify the wording so they can be interpreted with the correct meaning. In addition, to prevent the recurrence of problems like this incident, we will establish a system that not only checks the overall logic of probability systems in game but also checks the actual application status of probability type systems in-game in real-time.

    Current Probability Type Systems’ Inspection Results and Probability Type Systems’ Monitoring System Build Plan

    Star Force enhancements are periodically verified based on usage logs and it has been confirmed that the system is operating without significant differences from the rates shown in-game when checked statistically. This part can be checked through the below statistics of all Star Force enhancement attemps from the second half of 2020. These are the results excluding 100% chance on 5/10/15 stars events, Chance Time attemps, and Superior equipment enhancing. This is a probability table showing the total attemps and results with the destruction prevention option disabled and passing/failing star catch. When you successfully star catch, the success rate is applied at 1.05x the original rate. (Based on succeeding at star catch at 15 stars, the success rate is 31.5%, the maintain rate is 66.45%, and the destruction rate is 2.06%.)

    No Destruction Prevention, No Star Catch
    [​IMG] [​IMG]

    No Destruction Prevention, Star Catch
    [​IMG] [​IMG]

    The left tables show the Fail (Decrease) rate and Success Rate, the right tables show the Destruction Rate and Fail (Maintain) rate.
    The three columns below each header are from left to right: the number of attempts, the planned rate, and the actual rate.​

    These are probability graphs showing the attempts at Star Forcing at 15 stars with passes and destructions. Only 100% chance on 5/10/15 stars events were excluded.
    [​IMG] [​IMG]

    The verification of actual result values for the rates of paid probability type items posted on the homepage is automated. The actual result values are verified on a daily basis, and the abnormal detection system operates if there are abnormal values. Since the error on January 28, 2021 where Luna Crystal pet data was omitted, we now count and detect abnormalities every 30 minutes for the first day of sales of paid probability type items.
    [​IMG] [​IMG] [​IMG]

    In the future, we will create an environment in which you can enjoy the game with confidence by establishing a monitoring system for the probability type systems in-game.

    For users that have been unable to use Rebirth Flame items as intended due to the current additional options error, we will look into the usage history and provide compensation as soon as possible. In addition, the ‘problem where jump and % all stats appear together frequently’ has not been fixed on the official server, so we will include Rebirth Flame items used after this announcement in our compensation.

    We apologize once again for disappointing those who have sent us a lot of support, and going forward, we will repay you with updates that are more satisfying.

    Thank you.
    MapleStory’s Director Kang Won-ki


    To illustrate why things like jump and % all stats appear together more frequently, I made a quick example. Based on the logic provided in the letter (albeit a little simplified to make it easier to see), we can follow these steps:

    1. Choose 1 option randomly (DEX+INT).
    2. Separate the list into two sections, below and above the first selected option (dark green and light green). Note that you cannot get the already selected option (DEX+INT) again.
    3. Choose one option from each section randomly (LUK – 2A and Attack – 2B).
    4. Choose one of these options randomly with a 50% chance (Attack – 2B).
    5. Repeat the process, separating the list into two sections (sky blue and dark blue). Note that you cannot get the already selected options (DEX+INT, Attack) again.
    6. Choose one option from each section randomly (DEX – 3A and Jump – 3B).
    7. Choose one of these options randomly with a 50% chance (Jump – 3B).
    8. Repeat the process, separating the list into two sections (indigo and blue). Note that you cannot get the already selected options (DEX+INT, Attack, Jump).
    9. Choose one option from each section randomly (STR+DEX – 4A and % All Stats – 4B).
    10. Choose one of these options randomly with a 50% chance (% All Stats – 4B).

    As you can see, when jump is chosen as an option, the only stat in the section below it is % all stats. Therefore, when the next option is chosen in the next step, there is a 50% chance of getting any of the stats above it and a 50% chance of getting % all stats.


    In addition, after this letter was released on the MapleStory homepage, players focused on the fact that the Ability system also has a similar probability system to additional options, and they found something very interesting. By locking various combinations of lines on your Ability, you can get other lines at a much higher rate than usual. For example, many of my friends got critical rate on their second line (which is extremely rare) by locking prime line magic attack and all stats on a lower line then rerolling. I actually tried this myself and funnily enough, before I got either of those pre-requisite lines, I straight up rolled critical rate lol.

    There are a lot of different combinations for various desired stats such as critical rate, buff duration, attack speed, and boss damage. Other versions should be able to use this strategy as well, assuming the Ability system works the same. You can find a lot of resources on Korean sites such as Maple Inven. They’re calling them ‘recipes’ haha.

    Source: Orange Mushroom's Blog