2p stands for second player, and is usually used in videogames. If you have chosen a character, and the second player chooses the same one, there will be slight differences in the characters such as clothing or colour schemes. In the anime Axis Powers Hetalia, the term 2p is used to describe alter egos of the characters, who are usually darker versions.
2P Italy is so adorable, I just wish you didn't have to worry about him murdering you in your sleep.
2p by Fandoms Over Sleep June 10, 2016
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