Easter eggs in Barony come in the form of Minecraft Pickaxes that float and rotate in midair, accompanied with flavorful text. They don't appear to do anything other than to occupy hidden places in the game.
You can find a Minecraft Pickaxe on the floor 3, in Minetown. It's placed in a room that is hidden in the left corner of a water pool, that stands behind a bunch of closed gates. You'll have to use telepotation or a pickaxe to enter that pool. There is also a lever behind gates, it opens a one of these gates.
You can also find the Minecraft Pickaxe hidden in a corner of the Gnomish Mines
Filly Rainbow Dash
An image of filly Rainbow Dash from My Little Pony Friendship is Magic, can be found on the map named "boss"
(floor 20) It's a small wall decoration that's hidden, off to the side of the level over a pit and behind some walls. It can only be found via ring of levitation or through the game editor. The magic talking mace Sharur will also sometimes say "Rainbow Dash is best pony, it's true!"
Brave Sir Robin
Wandering through the various levels you find tombstones here and there, sometimes they spawn ghouls when you right click on them, but sometimes they just read out a funny or clever "RIP message" (rest in peace). Once in a while a tombstone might say "here lies brave Sir Robin, he bravely ran away", this is clearly a reference to Monty Python and the Holy Grail.
Ocarina of Time Letter
Occasionally a scroll will turn out to be a piece of mail, one possible outcome of what is written on the piece of mail is "Help me, I am waiting for you inside (781) Lord Jabu Jabu's belly. --Ruto, PS: Don't tell my father!" Which is a reference to Legend of Zelda's Ocarina of Time, the part where you have to rescue Princess Ruto. As to the "781" it would seem to be some sort of glitch.
Brocks' Best Line
Upon reading a piece of mail, you might find a quote from lovable old Brock from Pokemon! Brock's supposed best line of, "I know! I'll use my trusty frying pan, as a drying pan!", is a possible outcome message of a piece of mail.
Dev Random Names
When you click, "Random Name" in the name menu of the character creation, there is a possibility of the names, Sheridan the Glorious, and Josiah of Lords. This is referring to the Sheridan Kane Rathburn, the Team Leader, Programmer, and Designer of Barony, and Josiah Colborn, the Community Manager and Art.