Rapidash

Type Tier
Fire UU
Statistics
Stat
HP
65
333
Atk
100
298
Def
70
238
SpA
80
258
SpD
80
258
Spe
105
308
Name Item

Standard Rapidash

Leftovers
Moveset
~ Fire Blast
~ Return
~ Hypnosis
~ Hidden Power Ground / Hidden Power Rock

Meh. No wonder this is UU. Fire Blast gives Rapidash some extra kick behind its Fire attacks. Return and the Hidden Power run off its best attacking stat. Hypnosis because there's not a whole lot more Rapidash can do.

Name Item

Cursing Rapidash

Leftovers
Moveset
~ Curse
~ Fire Blast
~ Return / Iron Tail
~ Hypnosis

Might be good for a laugh and to catch people off-guard. Stopped cold by Rocks, though, which is why Iron Tail is an option. Sleep what you can't beat, and Fire Blast whatever resists your physical attack.

Other Options

Reflect is a good option because it can help Rapidash live a bit longer. Double Kick can be a nice alternative for Hidden Power Fighting if you don't want to hurt your attack stat by using the Hidden Power (10 less Base Power, but at least you'll have a few more attack stats). Charm can be good against the Cursers. Sunny Day can help that somewhat mediocre Fire Blast.

Opinion

It's a Fire-type. Not a very good Fire-type either. Its best stat is Attack but it doesn't even get good moves for that stat. Earthquake / Magnitude would have fit perfectly on a Pokémon with hard hooves. It suffers from the same thing most Fire-types suffer from: poor movepool and stats allocated in the wrong places. It might be able to do some things in the OU metagame, but Charizard is better in every way.

Counters

Rapidash is very limited in terms of move selection, so Rock and Water Pokémon are excellent counters because they resist its main offense, Fire Blast. Snorlax takes next to nothing from Fire Blast and will usually win a Cursing war. A sturdy Pokémon with Sleep Talk will usually stonewall Rapidash, as it renders worthless what is arguably its biggest asset, Hypnosis.