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.

v. collectively or individually finding someone/something to blame for a problem, as opposed to brainstorming which connotes finding solutions to a problem

n. the act of finding someone/something to blame for a problem

(from a TV ad for HD television)

2P stands for second player and is mostly used for videogames where if someone picks the same character as you yours will be different. And in 2p!talia (2p hetalia) is where characters who are usually friendly and nice are now cold and mean and mean are nice, things like that.