What is an Easter Egg?
An Easter Egg is a special type of issue that nations can only ever encounter once. They're meant to be jokes and references about NationStates that would otherwise not be suitable in a normal issue. They also often have strange and esoteric requirements before being able to receive it. Because of the requirements I just mentioned, it can be difficult to pin down exactly what triggers an Easter Egg. The explanations in this post are as accurate as we as a community have been able to determine, but please keep in mind that this post might not be 100% accurate.
It is advised that you wait until your nation has at least 1 billion population before hunting for Easter eggs. Many of these issues require changing customizable fields and as such smaller nations are often unable to meet the requirements. Furthermore, many of these issues also seem to have a population requirement somewhere around 1 billion, so even if you're able to fill in the fields correctly, you might still be too young to be eligible. This seems to be an intentional mechanic as it ensures only experienced players who can appreciate the content of the Easter eggs will receive them.
Good luck, Hunter.
#77: World To End, Or Possibly Just Mark Anniversary
#78: Should We Pull The Lever? [Meddlers; ed: SalusaSecondus]
#80: Aliens Wish Peace/Trade Agreement [Exiled; ed: SalusaSecondus]
#215: What's Your Favourite Colour? [Antioch and the East; ed: Sirocco]
#223: Zombie Attack! [Naliitr; ed: Sirocco]
#256: Suburbs Are Out Of This World [Scolopendra; ed: Sirocco]
#266: Breaching the Great Fourth Wall of @@NAME@@ [Reploid Productions; ed: Reploid Productions]
#375: Keep Your Hands Off Those Lucky Charms! [Vile Island; ed: Sanctaria]
#408: Pony Peril [Sedgelight Sparkle; ed:Sedgistan]
#430: Please, Sir, We Want Some More Issues [Eta Carinae; ed: Luna Amore]
#471: Red Sleigh Down [Nation of Quebec; ed: Sanctaria]
#622: A Holiday Masquerade [The Grim Reaper; ed:Lenyo]
#1122: Just Say No to E [Zwangzug; ed: Zwangzug]