FEAR is a gimmicky strategy based around using a focus sash and getting to Pokemon to 1HP with endeavor, and then using a priority move like extreme speed to defeat it. It stands for
F ocus Sash
E ndeavor
Quick A ttack (because FEQR isn't a good acronym, and the most common priority used)
R attata (the most common user of this)
These Pokemon are also usually level 1, in order to maximize the chances of them going to 1HP on their focus sash. Despite Rattata being in the acronym, Smeargle and Aron are more popular users of this due to Smeargles set unpredictability and Aron being able to do this on repeat due to its ability sturdy giving it an in-built focus sash so it can hold a shell bell and go back to full HP due to the massive HP difference.
Its not foolproof, however. Psychic terrain blocks priority moves, preventing the priority from functioning correctly. Stealth rock and other hazards also completely shuts this down by doing some damage upon switch-in, preventing the focus sash from working. Ghost types are also immune to endeavor.
