F.E.A.R. Originally meaning F***ing Evil Annoying Rodent, now more commonly known as Focus sash, Endeavor, quick Attack, Rattata.
A lvl 1 Rattata holding a Focus Sash is put into battle against a lvl 100 anything. Rattata's first move is Endeavor and the opponent uses an attack to easily kill this puny, not-a-threat rat. The Focus Sash allows the Rattata to maintain 1HP. Endeavor then kicks in, making the opponent's HP equal to Rattata's: 1HP. Rattata's next move is Quick Attack, allowing a lvl 1 rodent to KO a lvl 100 beast with ease. (Rattata's not the only pokemon that can pull this off. In fact, there are several better ones that are not stopped cold by Ghost-types.)
Ruby's probably not THAT bad at Pokemon, she just met up with a trainer who likes to take cheap shots.