The Predator in Tom Clancy's: Ghost Recon Wildlands.

When I found the first green blood splatters, I was like: "wait a minute, isn't that?...nah, it can't be..."
When I found the skinned bodies hanging from the trees, shivers run down my spine.
When I stumbled over the crashed spaceship, I was totally giddy.
When I heard the clicking noise...I was like: "oh yeah...here we go, baby!"
And when I finally encountered him - I died basically instantly. XD

Not that that kept me from trying again.

For me? It was during very early City of Heroes.

One of the most interesting areas of the game was Faultline because of a very large inaccessible area in the back of the zone. It had a large lake of water and a structure clearly meant for future events. Most folks assumed it was future planned content and would become accessible at some point (which is what happened many issues later).

I was one of the first players to get into that area long before the update launched.

After some trial and error, I found a hole in the transparent wall and got into the inaccessible damned/lake area. I got to fly around and see all of the unfinished elements. After trying it a few times to make sure I got it, I message the devs and walked them through how I did it so they could patch the hole.

It was a fun secret area that I got to explore that was clearly still in development for a future trial. One that only a handful of us ever got the chance to enter before the official launch.

My favorite video game secret is the ghost train from Red Dead Redemption 2. It always gives me the chills when it goes by randomly, love it.

My favorite secret is: ABACABB aka the blood code in Genesis' Mortal Kombat. I got it from my brother's piece of paper and including all the fatality, that was so cool and gnarly!

My favorite Easter egg is a classic mgs1 where you the game was able to read your savegames.

It has to be the Arc of the Covenant from Raiders of the Lost Ark in a Nazi base in the first Bloodrayne Game. It was such a big surprise to me I had to stop playing and tell everyone that was in the house all about it. I'm so glad that easter egg wasn't spoiled for me before hand.

Game that i love is witcher series and red dead redemption 2.Most beautiful visual/Graphics till this date are present in this game.Most hyped easter egg i found in red dead redemption of bully 2 reference and for the Witcher 3 easter eggs ohh they never end .But the best one is vivienne found dead after 7 years of in-game time,the level of detailing present the game is awesome.Both of this game presented us choices and as we all know choices have consequences, and its leads to something disastrous or marvelous.And i also love the game no man's sky because it provide the vastness of universe,how tiny we are compare to this universe. But through our knowledge we achieve greatness in this vast universe.

Of course being able to play Maniac Mansion in Day of the Tentacle. An entire video game that serves kind of like a prequel to the one you're playing crammed into the very same one for free with saves and everything is simply the cherry on top and I'm most probably not alone with first finishing that Easter Egg before going on with the "main" game.
Good Times.

The Summoning (1992) on PC

There was a secret in the beginning where when talking to an introduction character there was a secret phrase (zebu) you could give that would open up an area containing end game gear and then a teleport taking you to the end of the game.

Man I wish this game was here.

Mine would be the Vivienne Easter egg in The Witcher 3 : Wild Hunt. The Easter egg where you remove her curse and she will have 7 years of life. Eventually, after spending 7 years in the game, you will find her dead body in Skellige.

My favourite has to be the hole + bucket ending in the stanley pariable, if you fall into the hole whilst holding the bucket you will get a unique ending cutscene of the two staring a life inside the hole and creating a little home with a kitchen, sofa tv ect.

My favorite Easter Egg is Reptile in Mortal Kombat. For years before the internet was a treasure trove of useless information and porn, there were only rumors between friends and gaming magazines to unlock secrets in games. We'd play the game and play the game, feeding quarters into it. And eventually after we were done, some guy would show up and unlock it and we'd watch in awe. Now, it's apparent how to do it. Double Flawless victory and fatality on the Pit when there are shadows over the moon. But the fun of hunting it down and the joy at finally figuring it out (never mind the pocket money we blew through) was the real secret. We had so much fun trying to figure out this game secret, that it was almost disappointing afterward.

The Easter egg/thank you note left by the developers of The Darkest Dungeon in the last dungeon, before the final boss; having supported the development of The Darkest Dungeon on Kickstarter, it felt highly personal and rewarding, reading those few words, knowing that I had helped, in however a small way, so that this brilliant game could exist, generating lots of memorable quotes that are bound to become Easter eggs themselves, sometime in the not too distant future.

Cavemen can be found in Halo 3 and ODST. They are in three locations in Halo 3. Once in a cinematic in ODST. All the Cavemen faces are the same, but the body sizes are different. If you shoot them, they will bleed but not die.

The original floppy version of Secret of Monkey Island and the stump on Melee Island with the missing disks gag. When the game went to CD-ROM they had to take it out but you can find screenshots online.