This page lists the Easter Eggs in HITMAN™ 2.
The Weight - Standing on a scale in the downstairs of the house shows a weight of 47kg. This occurs with every bathroom scale you find.
Dolphin Exit - When holding a fish at the fountains near the Kronstadt Center, the pattern of the water spouts will change. When the pattern is retraced by the player, an exit will unlock near the dolphin statues. Exiting that way will result in Agent 47 riding off into the sunset, standing on two dolphins that carry him away from the mission area.
Secret Flamingo Exit - While wearing the flamingo disguise, go to the nest on the Kronstadt helipad to discover a secret exit.
The Stig (Top Gear) Exit - While in the Pale Rider disguise, eliminate both your targets, then head to the Kronstadt pit exit. This triggers a short, humorous line from Diana about 47 and his exploits before you race off, similar to what Jeremy Clarkson would say about The Stig in a segment of Top Gear.
SpongeBob Reference - A SpongeBob reference can be found within the aquarium in the Kronstadt building.
bigMooney06 Reference - When you kill everyone in Miami, the PA system will congratulate you on killing everyone in Miami and calling it a "Global Fucking Genocide" with a thick Scottish accent, a reference to the Hitman YouTuber bigMooney06.
Mary Poppins' Exit - If you shoot down the Yellow Umbrella from a nearby fishing village, it will fall in the river and stop at the boat shack, then you can exit via it and get a unique exit.
Fernando's Cello - In Rico's mansion there is a cello, which was played by a Blood Money target, Fernando Delgado. And a bonus fact about how Rico vows to kill his uncle's assassin, who is everyone's favourite bald assassin: Agent 47.
GoldenEye 64 - In the ruins by the hippo enclosure, there is an explosive, resembling a proximity mine from GoldenEye.
Items from PUBG - Items from PUBG are found in a villager's house.
James Bond - an NPC will speak in a voice from a James Bond movie if a fusebox is disabled.
Rick & Morty - All around the area of Mumbai are Schwifty-branded products.
Hitman 2: Silent Assassin/Sapienza - In the arcade room on the computers, there is the menu screen of Hitman 2: Silent Assassin and a picture of Sapienza.
Zelda's Rupee - On the beach between the entrance to the crows HQ and the barge, you can find a breakable pot and if you break it a coin (rupee) drops, like in The Legend of Zelda.
Clint Eastwood - Wearing a certain costume can cause an NPC to think 47 is Clint Eastwood.
Breaking Bad - A pizza can be found on a roof, like in Breaking Bad.
Ninja Turtles - A pizza can be found in a sewer drain.
Dino Bosco - In the Wilson property on the TV that is switched on, part of the news story program has the Film Festival being in memory of Dino Bosco, a reference to The Icon.
Isle of Sgàil
Monty Python - Two guards on the east wall in Skáil debate the appearance of a coconut, with one of them convinced it was carried by a swallow who gripped it by the husk, which is a nod to the movie Monthy Python and the Holy Grail.
Oingo Boingo - If attempting to enter a restricted area without the correct disguise, a guard may state "All dressed up with nowhere to go?", a reference to the song Dead Man's Party by the band Oingo Boingo
Uncharted - When reading intel on the twins in the mission plan menu, theres a mention of a treasure hunter named Blake Nathaniel. This may be a reference to Nathan Drake from the Uncharted series.
Space Invaders/Atari In the IT department, one of the IT guys wears a shirt that says "Atahari" with a Space Invaders logo. This is a reference both to the Atari brand and to the Mata Hari, a famous German spy during World War One.
The Weight - Standing on a scale in the bathroom of your resort house shows a weight of 47kg.
SpongeBob Squarepants - There is a pineapple and what appears to be a coral beside it.
Moosenado - If you set up and meet the proper criteria, you can trigger a Moosenado to occur. For context, a moosenado is a tornado with moose spinning in and around it.
The Dundee Achievement - If you shoot all blow-up crocodiles on the island, you escape on the back of a blow-up croc, a subtle reference to the film Crocodile Dundee.
The Fourth Wall - going near a guard while being disguised as a guard can prompt that guard to say, "Yeah, you're totally the real one."
Dracula - a random NPC can say something along the lines of "Hey, Dracula, there's gotta be a better place for you to nap" when 47 exits out of a container. 
Animaniacs - A challenge in Sniper Assassin - The Last Yardbird is titled "Are You Pondering what I'm Pondering," in which you shoot 2 mice. This is a reference to Pinky and the Brain from Animaniacs.
The Yardbirds - A challenge in Sniper Assassin - The Last Yardbird is titled "Psycho Daisies," which is a reference to the song Psycho Daisies by the band The Yardbirds.