I think my favorite thing about the more recent seasons of Red vs Blue is knowing that someone had to play through the Halo 4 campaign solo on Legendary to unlock the original Mjolnir helmet just for Caboose.
1) Infinity, after encountering the Spartan-Ivs, Lasky, and Palmer.
Cortana: “A topographical scan of the area shows a break in the foliage north of here, should be big enough to bring in a dropship for evac. Of course, I don’t know how many Spartans they can fit on there…”
John: "You noticed that too, huh?“
Cortana: "Apparently we were easier to replace than to rescue.”
2) Infinity, when you get the Mantis.
Cortana: “Just how you like them: big, ugly, and overflowing with machine guns and rocket launchers.”
3) Reclaimer, upon entering Librarian’s Rest and encountering the Sentinels.
Cortana: “Chief, hold up. Those Sentinels are still the same blue colour as the ones we saw earlier, before the Didact took control of the Prometheans.”
4) Reclaimer, after the Librarian snatches Cortana from the system.
Cortana: “Chief, get me out of here!”
Librarian: “Your ancilla is safe, Reclaimer Use of your armour’s neural link is required for this simulation, and so separating you was a necessity.”
5) Composer, just after Cortana crashes the Lich into Ivanoff.
Cortana: “I’m sorry - I just… can’t stop them. It’s like a thousand of me arguing all at once!”
John: “I know–”
Cortana: “That this station is already lost? That we’ll never find Halsey?”
John: “You got us here. That’s all that matters.”
6) Midnight, going through the gravity lift towards the final area.
Cortana: “Chief… The Didact… he’ll be out there, won’t he?”
John: “Focus on the Composer. If we face the Didact, we’ll find a way… together.”
Cortana: “And if we can’t? John… I don’t know if I’m ready.”
John: “Nobody ever is, Cortana. But we all reach the end, some day.”
Cortana: “No, John… it’s just that… I’m just not ready to lose you.”
7) Midnight, just as the Didact begins to power up the Composer.
John: “Cortana, something’s happening!”
Cortana: “The Composer… it’s preparing to fire!”
Cortana: “If we can just reach the Composer’s controls, maybe I can–”
John: “No time for maybes, Cortana. It needs to be stopped at any cost.”
Cortana: “John… you can’t mean…”
John: “I think we both knew this was a one-way trip.”