From Nookipedia, the Animal Crossing wiki
In Animal Crossing, he takes the mail after the player has sent Pelly or Phyllis five letters. He flies down towards the player's house at 9:00 AM to 5:00 PM to deliver mail and lands by the bulletin board. He will walk to each letterbox and place mail inside of each one, unless disturbed by the player, whom he will talk to. Once the mail has been delivered, he will take off and fly away within two acres. His love for Phyllis is often talked about among the villagers.
He continues to be the mail carrier in Animal Crossing: Wild World, but with a slightly different role. In the game, he cannot be seen delivering the mail, but can be seen flying above the town where he can be shot down with a slingshot at exactly 9:00 AM or 5:00 PM on random weekdays, and he will not be aware who shot him down. He will not appear during rain. He can be found near the player, laying face down. He will proceed to get up once talked to. Once he is shot, the player will not be able to move until he falls on the ground.
His relationship with Pelly is complicated in comparison to other games. Pelly really likes Pete, but she does not think he likes her in return. In fact, Pete actually has a crush on Pelly's sister Phyllis, who in return hates him. Unlike in the first Animal Crossing, he has a higher pitched voice.
In Animal Crossing: City Folk, Pete appears walking around town at 5:00 PM to deliver the mail, at the same time as he did in Animal Crossing. He also appears when Nintendo sends DLC to a player. However, he randomly appears in the town, rather than flies in. He will only talk once to the player, when spoken to. Afterward, he only says that he has to get to work.
It is clear that Pete does not have feelings for Pelly in City Folk, but seems to be interested in her sister, Phyllis because she is more mature than her younger and nicer sister. When talking to him he blushes while mentioning that Phyllis' perfume smells "exotic," and giggles when he mentions that she said "good night" to him.
When he is in town, some villagers will start rumors about Pete and other villagers, some even suggesting they are in a relationship with him. If you listen to some of their conversations, snooty and cranky villagers will say how they have changed the name plates on other snooty and cranky villagers' homes to "Phyllis' House," usually involving this with other arguments, like giving other villagers fleas for revenge. Booker will not know when Pete is in town because Pete flies into town, rather than goes through the Town Gate.
He retains the same role in Animal Crossing: New Leaf as in Animal Crossing: City Folk; he can be seen walking around town at mail delivery times and delivering certain DLC, although some DLC in Animal Crossing: New Leaf must be claimed at the Post Office instead. He can let the player know if another player in town has a full mailbox, however.
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