I did this again with the new releases, no alicorn guide cause they're easy to tell apart, the standard brushables may not always be. I don't actually own Sweet Song, Star Dreams or the prototypes, but I'm 99% sure my guesses are correct looking at the other eyes, correct me if I'm wrong, check between the hair plugs if you own them and tell me the letters please! I assume this is useful for customizers who want a specific eye shape? The pegasus heads are rarely used, oddly enough. I only counted prototypes that were unique, and not frankensteined, I own none of them anyway so it'd be pointless. I'll only add more if someone tells me what molds they have cause I can't guess on them.
I guess this could be put somewhere for reference?
Edit: The info applies to all ponies with the name (meaning, all versions of brushable Pinkie Pie have the same head) unless stated otherwise.
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Applejack Head (AJ) Total: 10 (9 minus prototypes)
Applejack, Lily Blossom, Feathermay, Honeybuzz,
Flitterheart, Daisy Dreams, Sweetie Blue, Ploomette,
Star Swirl, Zecora.
Pinkie Pie Head (PP) Total: 11 (9 minus porototypes)
Pinkie Pie, Cheerilee, Cupcake, Plumsweet, Diamond
Rose, Minty, Sweetsong, Cherry Berry, Sunny Rays,
Flower Wishes, upcoming shimmery tinsel Rainbow
Dash.
Twilight Sparkle Head (TT) Total: 8
Twilight Sparkle, Lulu Luck, Twinkleshine,
Snowcatcher, Princess Luna (Canterlot only), Rainbow
Flash, Lyra Heartstrings, Trixie Lulamoon.
Rarity Head (R) Total: 7
Rarity, Dewdrop Dazzle, Starbeam Twinkle, Sweetie
Swirl, Cherry Pie, DJ-Pon3, Lemony Gem.
Rainbow Dash Head (RD) Total: 2
Rainbow Dash, Skywishes.
Fluttershy Head (F) Total: 2
Fluttershy, Blossomforth.
Scootaloo Head (SC) Total: 2
Scootaloo, Apple Bloom.
Sweetie Belle Head (SC) Total: 5 (2 minus
prototypes)
Sweetie Belle, Star Dreams, unreleased flower filly
unicorns (3, counting the earlier yellow one as one
of these).
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More details on the various head molds coming when I'm less lazy. I just redid this from scratch looking at Strawberry Reef and the ponies on my desk. I'm fairly picky and nerdy about this information, I may attach hair colors onto this some day when I'm REALLY bored. Yeah, other people did this before, but so have I, and I want to be thorough.