Easter Eggs
The developers have hidden multiple Easter Eggs in UnderMine and this is a page dedicated to keeping track of them.
Main Menu
Since version 0.6.0, the sky color depends on the players system-time. It changes to light theme from 8:00 am to 7:59 pm, and to dark theme from 8:00 pm to 7:59 am.
Holidays
Similar to games like Minecraft, UnderMine has code that detects the date that a player is playing on, and if it falls into a certain range of date certain changes are made to game.
Valentines Day
While it seems to have been removed in the 1.1.0 update for a while unused assets existed in the game for a pink bobo texture, which was probably added for a potential valentines day set of textures, back in the earlier days of the game the developers posted a tweet "Happy #Valentines Day! In case a handsome mustache doesn't do the trick make sure to bring along a charm potion. #indiegame"[1] However the 
Charm Potion is no longer in the game either, the asset was re-cycled for Kiss of the Succubus
Bobo skin.
Charm Potion effect.
April Fools
For April Fools Day in 2020 the developers created a update for the beta branch version of the steam game that had a modified version of 
Float Boots called 
Extra Float Boots.
Halloween
Since 2019 every year a couple of days before Halloween there are a few assets that change to celebrate the holiday, the changes are Pilfers wear Pumpkin Costumes, Black Rabbit wears a costume, and 
Canary becomes a ghost version. This skin can be activated at any time, by changing the date to between October 29th and October 31st.
Black Rabbit skin on halloween.
Pilfer skin on halloween.
Canary skin on halloween.
Thanksgiving
The developers mentioned in a tweet[2] that they have had plans to put a Thanksgiving Easter Egg into an update, however the assets are currently unused in the game files. The assets are for Brussel sprouts, Mashed Potatoes, and Turkey.
Christmas
Only on the 25th of December every year the assets for the Bobos change to Yeti versions and the Pilfers wear Santa hats. Black Rabbit also has a Christmas Costume. This skin can be activated at any time, by changing the date to December 25th.
Pilfer skin on christmas.
Bobo skin on christmas.
Black Rabbit skin on christmas.
References
- ↑ Happy #Valentines Day! In case a handsome mustache doesn't do the trick make sure to bring along a charm potion. #indiegame
- ↑ "A very late contribution from @SpyklesArt For all you west coasters, and the east coasters that haven't passed out from turkey comas yet." – @undermine_game on Twitter