Easter Eggs

Colosseum

There are three secret bosses in the Colosseum that can be accessed with special items. The statues for them lie behind the door at the end of the east wing. Once you have given one of the three items you can use the door. More details here.

TARDIS

A police box appears extremely rarely in game. The only place with pictures of this is Maggie's.

Tuskers

Orion revealed an easter egg in a blog about the 100th patch. - Link

You give Brighteyes, the Tailor Mushed Nanners.

Brighteyes, the Tailor says, "It's people! Mushed nanners is people!"

Brighteyes, the Tailor says, "It gets very lonely out here. I've had a lot of time to myself."

Violet Ball Interactions

Surloshen Realaidain:
You allow Surloshen Realaidain to examine your Violet Ball.
Surloshen Realaidain tells you, "So lovely! This would look great next to my lilies! But I cannot take that which is not mine. Good day to you, my friend."

Crystal of Life Protections in Chapterhouses:
You give Crystal of Life Protections Violet Ball.
As you press the violet ball against the crystal, it is slowly absorbed. You perceive no other effect.

From Missing Person Investigation:
You allow Guard Hrothgar to examine your Violet Ball.
Guard Hrothgar tells you, "Aha! A clue!"
Guard Hrothgar tells you, "Wait...this isn't a clue."

From Tanada House of Pancakes:
You allow Chow Doun to examine your Violet Ball.
Oh, come now - do you think we'd still keep adding violet ball interactions after we told the community that we were doing it? Err....apparently, we would.

You give Corpse of Pon Mi Violet Ball.
You plant the violet ball on the corpse. In a thousand years, archaeologists will stumble upon the corpse and think that the violet ball was the lynchpin to some horrible human sacrifice ritual.

You give Pon Mi Violet Ball.
Pon Mi looks at the orb, then at you.
Pon Mi tells you, "What am I supposed to do with this? Throw it at the Tanada who come to kill me?"

Other

The Golem Sanctuary dungeon has a hidden message in its map.