Something that dies to the abundance of Earthquake, Stone Edge, and bulky water types (or any for that matter). Rapidash has been my personal Worst Pokemon Ever. Sure, it's quick and even shiny (by the way, blue mane on Ponyta into silver mane on Rapidash...come on, really?), but it's really fragile and almost unusable in my small playgroup. Bounce helps, but only if it causes paralysis on the second turn, and it can learn SolarBeam, but doesn't work well with Rapidash's below average SpAtk stat.
Now if you're looking for an underdog, Farfetch'd is a boss.
Now if you're looking for an underdog, Farfetch'd is a boss.