Post-credit scenes

Throughout the Metal Gear series, there were scenes that appeared after the credits have rolled that usually reveal some stuff from behind the scenes or a plot twist.

Metal Gear
Big Boss contacts Snake via radio and reveals that he had survived their encounter, and vows that they will meet again, and that he will have revenge for his defeat. This is only present in the MSX2, Mobile, Subsistence, and Virtual Console versions of the game, as the NES version omits this.

Metal Gear 2: Solid Snake
Solid Snake, Colonel Roy Campbell, and Holly White are debriefed about the Zanzibar Land Disturbance, with Solid Snake refusing to rejoin FOXHOUND due to his being cured of his nightmares. He later tells them they don't need to run testing as the cartridge he retrieved was the right one. He then had it play on an MSX2 console, with Campbell confirming it, with Snake explaining to a confused Holly that they were able to confirm it was his due to the signature being backwards: VRAM 10K. After a brief discussion about how Kio Marv was ultimately a victim of a political game, Solid Snake inexplicably disappears from the scene.

Metal Gear Solid/The Twin Snakes
Ocelot makes a phone call to the President, and confirms that he succeeded in his mission to retrieve the REX data, and confirmed that, with the exception of Donald Anderson, whom he deliberately killed while making it look like an accident, no one suspected his true allegiance. He also verified that the FOXDIE virus is set to act within Solid Snake. Depending on the ending in the original version, he'll also reveal that Liquid had been misled into believing he had been the inferior clone, and that the president himself was actually a product of the Les Enfants Terribles project with the codename of Solidus, as well as confirm that they put a woman under surveillance. In the remake, this was included in both endings.

This game is also the first game in the series to include the logo of the game during the conversation, which would later carry on through the rest of the series. This was the result of an ad-lib.

Metal Gear Solid 2: Sons of Liberty
Otacon calls in and confirms to Snake that he had analyzed the data they had retrieved from Arsenal Gear, and revealed that one of the names of the Wisemen's Committee had in fact been one of their biggest contributors. However, he then tells Snake that, while he did confirm that the Wisemen's Committee had in fact been based in Manhattan, all of its founding members had in fact been dead for at least a century, with Snake expressing shock and confusion.

Metal Gear Solid 3: Snake Eater
Ocelot debriefed his KGB boss on the result of the mission, confirming the destruction of both Groznyj Grad and the Granin Research Facility, also informing his boss that the losses were necessary, as well as confirming the CIA had taken care of The Boss as agreed. He also agreed that the KGB act on disposing of Khrushchev, and also suggested that they use their knowledge of the operation and President Johnson's expectations that they keep a lid on the affair as blackmail for future negotiations with the US, before confirming that he'll keep the KGB informed. After hanging up, he then makes an outbound call, and then reveals that he was in fact a CIA agent as well, contacting the CIA Director. He then reveals that The Boss completed their mission and that the Philosophers' Legacy is in America's hands, also verifying that the microfilm that a Chinese Agent stole was a fake. However, he also confirmed that the Philosophers' Legacy was only half of the total amount, with Ocelot suspecting the KGB had the other half. He also verified that the Shagohod was destroyed, and that Groznyj Grad had been obliterated by The Boss via the other Davy Crockett they had brought in. He also revealed that he had intercepted the blueprints for a new weapon by Granin and was sending them to the CIA for a potential weapon for America, and inferred that Big Boss may have been partly responsible for it (also letting slip he knew him as John). He also confirmed that Khrushchev believed their cover story and that the second alert is rescinding on the Soviet's end, and that the Soviets neither realize he was triple-crossing them nor do they even know his true identity. He also verified that no one knows that he was ADAM, and confirmed that he'll still act as an agent for the new government, and that in the meantime, he'll be at the CIA's disposal.

Metal Gear Solid: Portable Ops
Ocelot receives a call from his employer, with him being surprised at the identity of the employer. He then confirms that he killed the CIA Director and made sure that it passed as a suicide, and implied that the CIA will have a major shakeup on their hands as a result. He then verified that he also collected the full legacy, and that thanks to his employer's leaking of the ballistic trajectory data to the director implicating him as the target, he went directly into his trap. He also confirmed that Gene's actually launching the nuke had not been part of their plans, and revealed that Snake had been their insurance policy. Ocelot also accused his employer of using him, and cited that he'll no longer serve him. However, after his employer revealed that he had battle data from the Perfect Soldier Project and implied that it involved soldier genes and genomes, Ocelot admitted that he could aid him in his project, although only under the condition that Big Boss join up so they could form the Patriots.

Metal Gear Solid 4: Guns of the Patriots
Otacon tries to hand over cigarettes to Snake, believing he had merely forgotten them. However, Snake revealed he deliberately left them behind as he intended to quit smoking. Snake then mentioned that he was going to make sure he sees the new world he had in effect created with the little amount of time he has left in life. Otacon then requested that he join him, largely so he could witness Snake's last days, although he also admitted that he also didn't want to eat Sunny's prepared meals alone. Sunny then requested that everyone come and see the eggs she had created.

Originally, she was specifically addressing Otacon and Snake to see the eggs, but Kojima had it changed so it would be ambiguous as to who she was referring to. The change was last minute, as it used the cinematics from the original line.

Metal Gear Solid: Peace Walker
The game featured two post-credit conversations, the first after the fourth chapter, and the second after the fifth.

In the first ending, Miller arrives at Big Boss's location and tries to get him to return (implying that he had stayed at Lake Nicaragua for a long time), citing that everyone was waiting for him. Big Boss then stated that he wasn't coming back, and cited that The Boss betrayed him with her final message, as she instructed him never to put his gun down. He then said he was following a different path, and eventually said he will be addressed as Big Boss from that point onward.

In the second ending, Big Boss gave a speech in front of various soldiers, informing them that they may have to undergo various dirty jobs, even support terrorism, and their actions may lead to them going to hell when they die, before formally renaming the Militaires Sans Frontieres as Outer Heaven.

Metal Gear Rising: Revengeance
Boris contacted Raiden, with Boris confirming that thanks to Raiden's actions and Armstrong's death, World Marshal was put to sale and the Sears Program was eliminated, although World Marshal itself was still in function, especially with the re-emergence of the War Economy. Raiden briefly recalled Armstrong's final words to him. Raiden also confirmed that he won't be returning to Maverick, and then cited that he has his own war to fight.

Halfway through, it shows Raiden, in a human-like body similar to his appearance in the opening, walking through a town, with four cyborg soldiers lying in wait to ambush him. As they ready to attack him, Raiden then materializes a container that is implied to contain his sword, and gives a brief smirk as his eyes shine red before the Rising logo appears.

Metal Gear Solid V: Ground Zeroes
Skull Face informs Paz that, thanks to the failure of his grand experiment, Zero had gone into hiding, with various Cipher agents getting their orders only from proxies, before pointing out that Paz was the exception to the rule as she actually met him in order to meet up with Snake, and thus she knew Zero's location. He then demanded that she tell him his location before telling her that he never knew freedom, and Paz was effectively free. She then asked if this knowledge would aid Big Boss and whether he would kill Zero for her. Although Skull Face inferred that it might help Big Boss survive, he made clear that he won't kill Zero, not for her sake at least. Paz then proceeds to tell him Zero's location after some hesitation.

This conversation can actually be found on Chico's sixth tape.