I only bring this up because of Mother’s Day, in the UK it’s on March 6th so hence my slight confusion (cleared up by Google, but anyway).
Are the holidays based on those in the USA? (AKA are there ones like Independence Day that don’t apply to other countries) or some other country?
IF the festival egg if for mothers day, the 2nd sunday of May is by far the most common day its celebrated on among countries. https://en.wikipedia.org/wiki/Mother’s_Day
Theres also a chance its for Golden week, which was recently if I recall right, since the game designers are living in japan.
I hope this helps some. 
They might localize the holidays based on language.
The current one does say Mother’s Day on the intro screen. I mean it might be golden week but I’m inclined to think otherwise.
Then again I know nothing of Japanese holidays.
The game follows American holidays as it did thanksgiving last year
So far the holidays have been
Thanksgiving
Christmas
New Years
St Patrick day
Valentine’s Day
Easter
Mother’s Day
And the next one would be Memorial Day on May the 30
Neomonsters is based in Tokyo and Seattle but they will use American holidays as they are more well known worldwide or maybe the Seattle headquarters deal with festival side of things and Tokyo is mainly for design and game development
I forgot to add we had a festival for android release so we might get one for pvp official release as well
Mostly US!
Ryan I commented on a different post about a glitch in the ultimate challenge and it’s happened twice now. Used protect teammates with cryogolem but enemies have still been able to single target my other monsters and I haven’t been able to use protect again. Both times it happened it was with cryogolem
Mostly? What holidays are used that aren’t US holidays?
I would say festivals to do with game like android and pvp release but we will have to wait till thanksgiving to see the full cycle
And they might do encore eggs for no reason and could be random
Will look into that!
Basically that 
For none festival eggs we do not attempt to pair them with holidays.
Aight, thanks for clearing things up