My favourite discoveries would have to be the Secret Dinosaur level in Command and Conquer and the Giant Ant level in Red Alert. I was happy that both levels were also left in the Remastered Collection!

Up up down down left right left right B A Start

I hardly ever even played Contra but if that's still stuck in my head 30+ years later, it has to be the OG.

GTA where you could walk into the statue and see the heart

Several easter eggs come to mind, but the main one that comes to mind is the rave elevator in Crysis 2. You activate a power box in the "Dead Man Walking" chapter, then go to a nearby elevator and call it, getting a brief glimpse of a couple C.E.L.L. operatives dancing in the elevator. Disco ball, lights, smoke- it's a whole party in there. I remember it making me chuckle the first time I saw it.

in hitman if you shoot coin man there underwear clap for you

Hello everyone and thank you for the opportunity!

Propably, I am none of the lucky ones either. Still, it is an interesting theme and quite a good read of the different suggestions, so far!

My favorite gaming easter egg (secret) usually would be one of those, which I happen to find by myself--such as the one in Gothic 2 climbing around to get behind the orcish siege wall (see: attached pictures 01 and 02).

The huge impact did not came only from its 'fourth wall' breaking (albeit funny) subversion of the whole premise of imminent danger in the game, but further more from my association with a similar scene in the excellent movie "The Thirteen's Floor", where at one point the protagonist decides to do something totally unexpected (driving through a road block outside the city and continuing onwards) until he reaches the literal 'end of the world' (in raw wireframe)--realizing his own world is merely a simulation, as well! (See: picture 03)

Unfortunately, it has been mentioned by 'Klassy Kitten', already. Hence, I am going for another one, which I have not seen in the comments, yet:

My pick is the the original "Prince of Persia" game (from 1987) unlockable and playable in its entirety within the initial console version, for instance on the Playstation 2, of "Prince of Persia: The Sands of Time" (2003).

The here on GOG.com available PC version does not include this secret--the wall to access the secret area is unbreakable, rendering the gate behind of it unpassable.
But it includes another secret accessible by means of a cheatcode in the opening scene on the balcony. A functional 2.5D re-creation of the first level of the original game with an easter egg room at the end with some merchandizing references and an image of the 'Sands of Time' development team.

( For a more recent example, I could name the game "Lumo". A fantastic love-letter to the 'pseudo'-isometric platform adventure games from the 80's, such as 'Knight Lore', 'Alien 8', 'Head over Heels' or 'NES Solstice' among others. "Lumo" is full of minor and greater references and many homages to those games, movies and pulp culture of the era. However, most of them are not actually hidden, rather in plain sight on the obligatory path through the game. With a few exceptions like the integrated minigames which in fact are re-imaginations of other famous video games of the era, including e.g. 'Zaxon', 'Marble Madness', 'Q-bert' and 'Pacman' each with their own twist on their respective original formula. The biggest downside is, that you have only one shot at each of them per playthrough, and there is no way of directly accessing them individually ;-(. )

Good luck to everyone and thanks again for the good reads and reminders!

Kind regards,
foxgog

[Edit: link correction due to the bug in the forum software]

Dying Light, thriller zombies, also, mario level.

Silent Hill 2's shiba inu ending :)

Way back when Super Nintendo was the latest console, a games store in my Australian town had a Japanese Famicon SNES you could hire. I convinced my mum to hire it for a birthday present so that I could play the Super Mario RPG. I completely by accident discovered the sole Easter Egg in the game, which turned Mario into his Super Mario Bros. appearance.
It was my first Easter Egg and it would be years before I even learned the term Easter Egg to describe what happened. That's got to be my favourite.

My favourite Easter Egg in any video game has to be in Halo Infinite.

There's a door hidden away near one of the bases, and inside is an arcade machine of Halo Infinite playing a retro version of the Halo Infinite theme.

Fallout:New Vegas, you can find an indiana jone skeleton(fedora) in a fridge, referencing Idiana jones and the crystal skull. You would need the Wild Wateland Perk to find it.

Mi huevo de pascua favorito, se da en la pelea entre Solid Snake vs Gray Fox, del videojuego de Metal Gear Solid, de la PlayStation 1; el huevo de pascua sería, la presencia de una consola de la PlayStation 1, que se encuentra en una de las mesas de la sala donde se lleva a cabo la pelea.

When it comes to easter eggs the best game to look for is Duke Nukem 3D. The game is chock full of easter eggs with Duke commenting many of them like

*) Luke Skywalker hanging dead upside down in an ice cave ("That's a force to be reckoned with.")
*) the destroyed Terminator in the press ("Terminated!")
*) Indiana Jones dead in a cave impaled on a trap ("We meet again, Dr. Jones.")
*) a body of a space marine ("That's one doomed space marine.")
*) the bridge of the enterprise together with the captain's ready room and the REALLY ready room.

and many more.

I suggest having a look at them on YouTube.

At the beginning of System Shock 2 there is a basketball on the street right before you enter the UNN recruitment center/tutorial area and choose your class. If you carry that ball in your inventory through over half the game and score a basket in the gym on the recreation deck you get a special message. The most memorable video game easter egg in my opinion.

Favorite little Easter egg way back was probably in Warcraft where you click a guard repeatedly, the response changes from "My liege" and "Your bidding" to just "What?!"