General
- The Title Drop in "Homecoming" includes Musical Nod to the main Halo theme for a few seconds.
- During a battle in "Reckoning", Cortana urges Chief to change to his secondary weapon. He snaps, "I know how the game is played, Cortana!"
- When Chief is having dinner with Corporal Perez's family, her brother asks him if he plays a game called "Spartan Attack" and what his KDR (Kill-Death Ratio) is. Chief replies "I don't keep score."
Books
- The idea of the Spartans having their childhood memories suppressed is a reference to an offhand comment in Halo: The Fall of Reach, where the UNSC considers using "selective neural paralysis" to do just that before Halsey shoots the idea down as being too dangerous in the long run.
- When Cortana is first introduced, she says "When the game is over, the king and the pawn go into the same box." In The Fall of Reach, these were her first words when brought online, albeit in Italian, and was something Halsey's mother would say to her as a child when they would play chess.
- In the opening Flash Back of Episode 5, the teacher giving Halsey and Keyes a tour of John's school greets a young girl named Parisa. This is a reference to the short story Palace Hotel, where Chief encounters a marine named Parisa who he soon realizes was a childhood friend of his from Eridanus-II.
- Season Two opens with the reveal that major colonies like Madrigal and Harvest were attacked and glassed by the Covenant. These were the same major colonies destroyed before the Fall of Reach.
- Dr. Halsey being at the mercy of Ackerson was similar to her arrest and incarceration by ONI in the Kilo-5 Trilogy of novels after the events of Halo: Ghosts of Onyx, except in the books it was Admiral Margaret Parangosky and her successor Osman (the latter being a Spartan-II washout) who ordered Halsey's arrest.
Games
- During the attack on Madrigal, an off-screen Elite can be faintly heard shouting "Wort, wort wort!", a common victory cheer they would use in Combat Evolved when they managed to kill the player.
- The Heads-Up Display of Chief's helmet is directly modeled after the games' HUDs, largely blending Halo 3 and Halo: Reach styles right down to using the same aiming reticles and graphics for the various weapons and loadouts. The main difference is the show's inclusion of more interactive features such as facial recognition, target tracking, and the color scheme changing from blue to orange if the user is in combat.
- The sounds for the Elite's cloaking device and Chief's recharging shields are the same as in the games.
- The games' action mechanics are hinted at while being filtered through a more cinematic presentation. This includes overwhelming enemy shields with assault rifle fire before finishing with a headshot, Dual Wielding pistols, letting shields take damage until the need to Take Cover! to recharge, appropriating enemy guns and using a mounted turret as a handheld weapon.
- When entering a cave with strange shapes along its pillars, Kai remarks that the "cave network does not appear to be a natural formation", referencing Cortana's infamous line from the first gamenote .
- When Silver Team is flying to the Aspero system through the gravity anomalies, Vannak expresses concern that their Condor won't survive the maneuvers, to which John replies "It'll hold", repeating a line from the last level of Halo: Combat Evolved, there in reply to Cortana as the Chief pilots a falling apart Banshee.
- The armor suit-up sequence for Kai-125, Vannick-134 and Riz-028 shown in the first episode is nearly identical to a suit-up sequence for Spartan IV's in Halo 4's Spartan Ops intro scene, with the ringed frame they step into and the sequence of events in how each section is attached to the person.
- While the Mjolnir armor in the show are a reasonable approximation of how it looks in the games, in Halsey's main lab there are either prototypes or mock-ups of Mjolnir armor on display that hew slightly closer to the look of the games with more vibrant colors and simpler details.
- The second season episode "Sword" reveals that Sword Base is where the artifact MacGuffin from season one is being contained and the Covenant have already disabled a comm tower and compromised it. "ONI: Sword Base" was the second level of Halo: Reach and revisited in "The Package," revealing it was secretly protecting a Forerunner installation located underneath.
- The communications relay that Cobalt Team were sent to investigate, and that tips the Chief off to the Covenant being on Reach, is Visegrád Relay. In the first playable level of Halo: Reach, "Winter Contingency", this was the site where Noble Team were sent to and discovered that the Covenant were on Reach.
- Keyes mentioned a protocol named Winter Contingency, which is an official UNSC emergency plan that deals with situations where Covenant forces have become aware of, or are present at, a human colony world. In Halo: Reach, Winter Contingency was mentioned a number of times when Reach was being invaded by the Covenant even as the UNSC mount their counterattack.
