I was pretty surprised there were as many as there were. It’s a good way of showing how well written the game is that it wove those in. To list a few:
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The second level Foundation with this dark Forerunner structure surrounded by Storms is very similar to the Breaking mission in Halo 5. In that mission you hear distant thunder and obviously you find Cortana at the heart of this central area. This is directly referenced when the Pilot asks if this is a trap since that’s what it was in the Breaking. You also hear the same storm sound when you have the vision of Cortana later during the teleport part.
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On landing on Genesis the Chief is prompted by Cortana to activate several consoles that open the Domain portal. At one point she says “you already triggered most of the Activation Sequence. Just like I knew you would.” In Infinite the Weapon asks you activate several “Sequences”, with a soundtrack of the same name playing and keeps saying she needs more data to get this plan to work. This is why the Chief is incredibly suspicious of the Weapon cheerfully prompting him to do this.
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When you get all the Ring Forerunner Audio Logs a bit of dialogue plays where the Weapon says: “This is difficult to explain” to which the Chief says “Try me.” They say the exact same thing on Genesis when Cortana is trying to evade talking about her plan with “it’s difficult to explain. It will be easier when we’re face to face” to which the Chief has the exact same response. “Try me.”
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Adjutant Resolution making a new body to fight you repeatedly. The Weapon sarcastically jokes about how “that’s him dealt with again.”. This is referencing the Warden Eternal who had multiple bodies and kept coming back.
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Obviously crashed Guardian, Cortana humming in the whispers like at end of Halo 5, Chief dropping into the Pelican like Locke did. Pretty sure the Grunt Tower guy tries to ring a Grunt with the Arbiter to try jump ship. The marines also name drop the “Arbiters forces”.