Photos courtesy Lunamoth.
Step 1... Frizzy haired pony
Do step 3 and 4 several times.
Heavily applying conditioner and running a thin comb through the hair will straighten most minor frizz. I use Head's Up! conditioner for dolls. Fruity or floral scented shampoos and conditioners are also popular with collectors.
For worse frizz, wet the hair and liberally apply conditioner or fabric softener. Heat a flat iron on the low setting. Separate the hair into small sections and run it through the flat iron repeatedly until the frizz is fixed.
Do not use heat on color changing or perfume puff hair as it will melt.
Most common in beddy-bye-eye babies and newborn twins, pony mohawks are where the hair sticks up instead of laying against the neck. To tame this, wet the pony' hair, pull it down around the neck, making certain it is smooth. Fold a piece of paper towel over a few times and wrap it tightly around the neck/hair. Secure it with tape or rubber bands. Let the pony sit until the hair is dry, then remove the paper towel.
You want this type of hair to be poofy, but be careful not to pull the hair out when combing as it's delicate. You'll likely lose some of it, which is ok. If it's only a little you won't be able to tell. Wash and condition their hair with the same shampoos and conditioners you use on your other ponies. Their hair is supposed to be soft, so use tons of conditioner and leave it in for longer periods of time if needed. I've gotten reports that carpet cleaner like Resolve Triple Oxi will help whiten dingy, grayed perfume puff hair.
When a pony's original hair is just too far gone, replacing their manes and tails can make a huge difference. Here are some color matching guides: AeraCura's Custom FAQs, The My Little Pony Hair Color Matching Guide, The Lavender Lagoon Rehairing and the Colour Matching guide.
Photos courtesy Mandy85.
Lots of ponies were manufactured with what's known as "fading pink" hair. It's a shade of pink that easily fades when exposed to sunlight and may of these ponies now have white hair. It's easy to dye pony hair back to pink using Rit All Purpose Dye. This shade of pink was vibrant with a tinge of orange to it, you can see examples with MIP ponies such as this Lickety Split. To achieve this shade, many collectors mix a bit of orange or yellow dye in with the pink. Petal pink is what is commonly used. You can use either the liquid or powder formula.
Whitening toothpaste (paste, not gel) and Rit Rust Remover can all be used to remove tail rust. Scrubbing the rusty area with toothpaste and a stiff toothbrush is usually enough to clean it.
It's usually the metal washer that rusts inside the pony's body, so most collectors choose to remove this. If needed, you can also remove the metal clamp using needle nose pliers. You can replace the washer with a zip tie.
Photos courtesy BabyIceCrystal.
Sulky brand tinsel works well as a replacement for the original and can be inserted the same as doing a re-hair. Fabric and craft stores often carry it and it can be bought online.
Other methods include repeatedly dipping the hair in hot water and combing it until de-frizzed. Some collectors fix frizz by wetting the hair, applying conditioner or fabric softener, then ironing it with a clothes iron set on low. Here's a video showing the use of a clothes steamer to fix frizz.
Photos courtesy Truevampiress.
Here are sites where you can purchase replacement hair and several offer supplies such as re-rooting tools:
Dollyhair.com - Buyer Beware: There has been a lot of drama surrounding this seller about her customer service and personal beliefs.
Photos courtesy Cyberunicorn.
Elish2 made a youtube video about styling Perfume Puff hair: Brushing and Styling a MLP Perfume Puff
Puff hair can be difficult to dye some solutions may be, a vinegar treatment, salt, or a dye fixative. You may also have to leave the hair in the dye for longer than would be needed for regular nylon pony hair.
To re-hair a perfume puff collectors often use yarn or mohair: Rerooting Tutorial - How to reroot a doll with Yarn
Einhornbaby at the MLP Arena provides some instructions for re-hairing Petite Ponies: "Soften the glue with hot water, pull out the tail (careful, you dont want to pull the tailbow too!!) and make a new one where you cap the end that will go into the pony with some sticky tape. Then put some glue into the hole in the tailbow and carefully put it in. Its a pretty sensitive task since petites are small, but if you take your time it will look very nice afterwards."
You can use any shampoo and conditioner to wash and condition your pony's hair. Everyone seems to have their favorite. Fabric Softener is also a common product for conditioning pony hair. I use Twin Pines of Maine Heads Up! products on my own collection and lots of collectors also get good results with products for synthetic wigs.
Some ponies have gotten some really strange stuff in their hair over time. For more stubborn gunk, try washing the hair with Dawn dish soap or an OxiClean bath followed by shampoo and conditioner.
Petite Pony photos courtesy Marlin. Claw clip photo courtesy Nicole B.
Add dye to hot water, test the color with a piece of white paper towel. If it's too dark, at more water, if too light, add more dye. Submerge the ponies hair for just a second and repeat until you achieve the desired color. You may need to work the dye into the base of the tail with a toothbrush or comb. As long as you don't leave the pony's body in contact with the dye for too long it won't pick up the color. However, you are just submerging the hair, not the entire body.
Dip the hair in an oxiclean bath to remove excess dye and rinse with cold water to set. Photos courtesy Aimee T.