The smallest ponies of each generation.

[Ponybookworm]

There's me on my computer, kicking myself the SECOND I look just below the monitor!!! The Kinder Egg G4s!!!

[Leave a Whisper]

G3 Tiny Book Sweetie Belle is a tad smaller then G4 Blindbags.

[MintyMyndi]

Just took a shower, and remembered some more!

If we aren't going to count the G2 Petites, then the McDonald's ponies (the 1998 ones, at least) are narrowly beaten by a Sundance figure that was an "extra" with some things (and is frequently mistaken for a McD's pony at first glance). She came with a Toys "Я" Us exclusive Friendship Gardens CD-ROM bonus pack, and was one of three toys you could get with the McDonald's Happy Meal Girl doll by Hasbro (imagine being the kid who got the can of Play-Doh!). She has a molded mane and a brushable tail, but is all one solid piece, unlike the '98 McD's ponies, who are hollow and have separate heads/bodies. I actually own her, so I feel silly for not mentioning her! 

Lavender Lagoon shows what looks like the same mold mentioned above, albeit with a molded tail, in a French perfume box.

Speaking of perfume figures, according to Lavender Lagoon, there were French exclusive perfume figures of at least Sundance, Easter Sky Skimmer, Tender Nuzzles, Light Heart, Spring, Princess Silver Rain, and Floral. These also have molded manes and brushable tails. No size comparison is included, though.

I'm not sure how the 1999 McD's ponies (hard plastic with all brushable hair) stack up, but they look smaller to me.

Other figures shown on Lavender Lagoon without size context are a set of stampers, a Sweet Berry figure with a molded mane/tail that appears to be made of hollow vinyl (I could see this one being bigger, potentially a bubble bath bottle?), and candy tins with figures on top. There's also a watch with a pony with a brushable mane, made in a recycled G1 mold which I believe was used for Ballerinas and Sweetheart Sisters, if you want to count that.

And lets not forget plain ol' G2 babies, those things are downright puny! I don't have any, but I imagine they can compete with those mentioned above.

Stepping away from G2 (and extending the definition of "figure"), there was a Play-Doh mold of G3.5 Pinkie Pie (only referred to as "My Little Pony") included with the Toy Time Race board game. She was one of the "playable characters" that you could mold and potentially squish. I don't have her, but she seems less than an inch tall, and at the very least could compete with the Blind Bags.

EDIT: I forgot the Newborn Scootaloo that came with Sisters' Day Out! She is small enough to be carried by the mom pony (why didn't they name them?) and has no hair, just a headband!

[Taffeta]

Oooh. I forgot about the Kinder ones. They are quite small. In fact, those squishy whatever ones...they came in a capsule thing and were kind of like the mashems but not mashems?

I have Scootaloo and she is small enough to fit into the hand of one of my MH dolls.

I think the G2 McD ponies are bigger than the G2 babies but I can't compare at the moment. G2 babies are significantly bigger than petite ponies though...

[MintyMyndi]

I can't stop bombarding this thread; I've just though of more. Sorry if it seems like I'm trying to steal the spotlight.

Firstly, the G1s. I don't think any of these are smaller than Petites, but they may be the same size.
The Maia & Borges ponies, Bully ponies, and Comics Spain ponies are pretty small, aren't they? And how big are the "Pony Look" hairclips (Lickety Split and Posey with long yarn manes) from Italy? Don't know. I don't have any of them.

Moving to G4, how big are the figures that come with the Egmont magazines? Once again, I'm American, so I don't have any...
The Flurry Heart/My Baby mold figures are pretty dang small, a bit too big to be in scale with Blind Bag ponies, but a bit too small for brushables... They came with both. If you count them as part of the brushable line, they're among the smallest of that line, probably beaten out by Breezies (if you don't count the wings). I have some of each, but it's late here, so I don't wanna check.
Speaking of babies, didn't the Cake twins have a Blind-Bag-scale release? I imagine those were pretty tiny, especially since they weren't ambiguously sized with brushables in mind. I wasn't that into Blind Bag ponies when these were out, so I didn't get them.

Sorry again for remembering more things and potentially being annoying. I feel like a spammer, but couldn't resist sharing... I'm probably overthinking this.

[banditpony]

This page needs pictures next to a ruler!

[Ponybookworm]

I need to piccie my TS collection again. As well as all the afore-mentioned & a mashem, I have a TS CMC & she's pretty small... Kinder egg is still smaller. Egmonts are a bit larger than Blind bags

[Taffeta]

Firstly, the G1s. I don't think any of these are smaller than Petites, but they may be the same size.

But none of those are smaller than the surprise twins pony twins, who are also smaller than the petites. At least I don't think so - the Bully figures certainly aren't.

Unfortunately Naynie's twins are in storage so I can't do a photo against a ruler for them, or a comparison. Maybe someone else can.

I have a picture of Scootaloo, who right now is the smallest G4 I can offer, but I can't find my camera cable ><

Edit: Found it!
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Isi and Batsy included in the picture for scale purposes...and because I'm lazy.

[MintyMyndi]

This page needs pictures next to a ruler!

Done 
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Some of these are just there for scale, like the Teenies (and Bootsie has his curls!), but here are all the pony body types I own which may qualify for this honor... EXCEPT my Drink 'n' Play ponies. I couldn't find them. Maybe they're camera shy? I wonder why that might be...