Hello,

The droprate for holiday mounts increased but they are now dropable only on the first daily account-wide attempt
I tried to drop Great Brewfest Kodo which used to drop at 4%
I looked at the wowhead comments and found that the holiday mounts drop rates have changed so that they drop more often but can be attempted only once per day (account-wide)

Sources:
Wowhead comment
Blue post
It's related to Midsummer but the change is effecrive for all holiday mounts

Interesting... For the record, this is the relevant portion of the blue post:

We’re changing the way the loot system for the holiday boss drops work. We have increased drop rates significantly for the first boss kill on a single account. Only the first attempt on a single Battle.net account will be eligible to receive the item drop, however. For each subsequent daily attempt on the boss with a single Battle.net account, the chance for the item to drop will increase and continues to accumulate for each failed attempt. This change will allow players to spend less time working to earn a specific dropped item while providing an increasing opportunity to get that item during the holiday.

To decide what changes to Rarity will be necessary, it would be great to have more information:

• The post mentions only the Midsummer event boss; is there any source for this change applying to all holiday events?
• What should the new drop rate be? Rarity can't deal with two different rates for the same item, so the % shown will be off
• While the addon could track the daily completion, the quest IDs would need to be recorded (e.g., using QuestsChanged)

Getting the quest IDs might be the biggest annoyance. It'll take a year to see all events, and players need to submit the data.

Note to self: wowhead lists the dates for holiday events here: https://www.wowhead.com/events/holidays

Assuming all of the holiday drops need to be changed, could compare drop rates before/after the event? And for collecting the quest IDs, setting reminders for the starting date would be helpful. Then someone who's actively playing the game could submit the quest IDs displayed by the QuestsChanged addon. There should be enough people in the Discord server to handle this part.

There's probably no way to get the luckiness % right, unless Rarity learns how to differentiate attempts over time (very unlikely).