In a cool bit of retroactive continuity, a new easter egg put into Modern Warfare 2 Remastered fixes a plot error from Modern Warfare 3. Everything takes place on the infamous "No Russian" mission in a "blink and you'll miss it" moment that casual fans likely won't spot.
To prevent spoilers, I'll be discussing the details below the video.
For those that haven't played any of the popular Call of Duty games from the last decade, there was a moment in Modern Warfare 3 where protagonist Yuri is seen crawling into the airport where Modern Warfare 2's "No Russian" mission takes place. This moment was a flashback to show players how Yuri attempted to thwart antagonist Vladimir Makarov and failed.
Obviously, Infinity Ward hadn't planned for this when creating Modern Warfare 2, so Yuri wasn't seen in the original version of "No Russian." Thanks to this remaster, the plot error has been fixed and players can spot Yuri crawling to his death while working through the mission.
A similar easter egg was present in Modern Warfare Remastered. Modern Warfare 3 featured a flashback to the Call of Duty 4 mission "One Shot, One Kill" and had players control Yuri while he and Makarov witnessed Lt. Price's attempted assassination of Imran Zakhaev. In the remaster, players could spot the car with Makarov and kill him, earning the "Time Paradox" trophy/achievement. Again, this wasn't in the original as Infinity Ward didn't plan for it.
Source: YouTube