ABCD is the 61st cutscene in Run 3, if counting all of the prior hidden and optional cutscenes.
This is a minor cutscene in the Run 3 story, yet it is one of the longest.
After beating Launch Site C, a cutscene with the Duplicator accusing the Angel begins. The Duplicator says he cracked the code. He argues that the Angel named the tunnels A and C, but no B or D. He also says that he is trying to take the Child away from him. The Angel denies it. He says that he needs some time to himself without the Duplicator bothering him and says to go away. The Duplicator say will not go away until the Angel changes his plans.
He says that the Bunny is out because he is an animal, Pastafarian is out because the Angel hates common decency, and the Duplicator is out because he keeps on exposing the Angel's plans. The Angel and Child are the only ones left. A for Angel and C for Child.
After a few seconds the Angel starts laughing. The Duplicator says that this isn't funny. The Angel says that he is just following the alphabet. The Duplicator asks why he skipped Plan B, and he replies saying that he didn't. Plans A and B are both coming from Launch Site A, and C and D are both on Launch Site C. Then he says that they won't even need all the other plans. The Duplicator says that the Angel is arrogant for claiming to know the future. The Angel objects, saying that making four other backup plans isn't considered arrogant. He adds on saying that he is not taking any chances on the overall plan.
The Angel says that in 2.5 months they will meet up at Launch Site A and the Duplicator will not interfere while they are going home. The Angel wants the Duplicator to leave and the Duplicator accepts. The Duplicator then leaves, but first asks if they are really going home, why they aren't going the same way they came, and the Angel says that is Plan E, and tells the Duplicator to go away.