So cool! How hard is it to redo their hair? I love Monster High dolls, too.
Once you get the hang of it, it's not that hard at all! The best method is to cut all of the dolls hair off and soak the head/ neck in hot water for about a minute or so and then slowly try to pull it off (you might have to submerge it multiple times), without breaking the neck prongs. Once that's complete, take some tweezers or pliers and try to remove the hair inside the head. Again, submerge the head in hot water, it helps to loosen the glue inside. When I first started out (7 dolls ago), it took me about an hour or so to complete this process, I can now do it in maybe twenty minutes (actually, I'm becoming increasingly better at yanking off the head in one pull).
After that, it's easy to reroot it- simply cut the hair to the desired length (I wrap my hair around the long end of a DVD case to measure it) and thread it through the pores using a doll needle (being sure not to pole any holes in the face/ neck). Depending on how much glue there may still be left in the head, you might have to use pliers to pull the needle through (plus, after working on dolls for two weeks straight, your hands will kill you, so using the pliers is nice in that regard). Once the string is hanging from the neck, knot it and then pull it back towards the head. Viola, hair!
I find the process of rerooting being similar to how I sew hair onto a poppet, so I really like it, since that's my favourite part of poppeting.
I find that it takes about one small to medium sized ball of yarn to do an entire poppet (though this will vary according to how thick the yarn is- the thicker it is, the more you need- ask me how I know this ).
And I do, too (obviously)! I think that my collection is up to about 40 now (not including any of these custom gals).