the cave in borderlands 2 that references minecraft , not only has creepers from the game but has skins e a exclusive weapon that shoots arrows from the game , its kinda sick

GTA IV

The heart inside the statue of liberty

In Dead Cells, theres a room in one of the areas that has a bunch of insects pinned to the walls. Among those insects is the image of Little Ghost from Hollow Knight.

There's honestly too many to pick from, but since I was just talking about it with friends a few days ago: I really like "you aren't supposed to be here" signs, particularly the one in GTA3 where you can jump over a normally insurmountable wall and find one such sign hidden in a secret alley. In later GTA3 updates (Liberty City Stories on PSP, etc.) they kept the area but updated the sign to feature new messages, like "you must really love this secret!"

Fallout 2 is a mountain of easter eggs just like the first one. Finding the bridge keeper in the wastes was probably my favorite easter egg. Love Monty Python.

So basically loot boxes for the site. No thanks.

The cow level from Diablo 2, it was just the most absurd thing I'd ever seen at the time, and how people managed to figure out the Horadric cube recipe. And bonus, it was great xp and dropped loot, so there was reason to return to it over and over and keep enjoying it.

So many from the witcher 3 but probably, The Killer Rabbit of Caerbannog!!

But also the angle statue that follows you in the graveyard when your back is turned is terrifying no matter how many times I go back there just as creepy as the Weeping angles from Doctor WHO.

For my part, I would say an easter egg that I’ve seen in Drakensang: The Dark Eye.

When you arrive in Ferdok, having Dranor (the thief of the game) with you, there is a cutscene, just before you enter the city, where Dranor leaves your team saying that there was a “misunderstanding” some time ago in Ferdok and so he doesn’t want to be seen and recognized by the city guards. He also tells you that he’ll meet you later. After a while you learn that he is captured (by his own mistake!) and thrown into an underground dungeon, used as a prison.

Later his girlfriend Salina asks you to free him and tells you that there is another way into the dungeon. She learned that a nearby trading company has a rat infestation in its underground storages and, through that, there’s a path that connects with the prison.

When you reach Dranor’s cell, to your surpise, he says that (being a thief) he can easily pick the lock in his cell door and escape anytime! But he wants you to prove his innocence properly, so he won’t be accused again. After that, you bring proof to the head guard and she has Dranor brought to you.

The easter egg part is this: with Dranor in your team, if you visit again the cell where he was, you see a Dranor in the cell!! Then an amazing dialogue follows among the two Dranors (the one in the cell and the one in your team) and the player’s hero, about this being a developer’s error which must be fixed! The Dranor in your team wants this to be fixed and the Dranor in the cell doesn’t, as fixing this error would make him disappear! Then the error is fixed, the imprisoned Dranor disappears, and your hero and Dranor comment that such mistakes shouldn’t happen!

Samus Aran reveal!!!

I think it's Fallout 2: In the wasteland you find can stumble across s crashed shuttle that is clearly from Star Trek: ToS. You can find some empty hyposprays there, too.

The bed in Wolfenstein: The New Order, whereupon falling asleep you end up playing the first level in the original Wolfenstein 3d, complete with secret area, graphics, etc.

Deadly Premonition, major spoiler here but through the game you are hunting the serial killer known as "The Raincoat Killer". At the end it is revealed to be the towns sheriff. There are countless clues throughout the game hinting (or out right revealing this) but you are mostly oblivious to them on your first playthrough. However his cars licence plate reads:

HESTHE1

or literally "He's The One". Its screaming it at you the whole game and you just never see it until later playthroughs.

There's a secret level in the original Star Fox for the Super Nintendo.

In the asteroid level on the right branch of the star map (the "hard" mission path), you fly past two large asteroids that appear different from the others in that level. At first glance, they appear to be indestructible, but if you shoot enough at the asteroid on the right, it will release an egg that hatches into a giant bird. Flying into the bird will warp you to a new location that appears as a white "rip" in the star map called "Out of This Dimension."

This is a trippy level with a quirky soundtrack, a distorted background with smiling planets, and where all the enemies are paper airplanes. The boss is a giant slot machine that uses a jazzed-up version of "When the Saints Go Marching In" as its theme music; to win, the player has to score three sevens (7-7-7) on the machine. Doing so finishes the level, but also traps the player in an endless loop, forcing them to reset the game.

You can see it here.

In Star Saga: One - Beyond the Boundary, the names of the crew of Vanessa Chang's ship were derived from the names of the people who worked on the game (such as Walter Freitag being mentioned in the game as Walter Friday).