Mountain Boy Ponies
The Mountain Boy Ponies were a huge leap forward in independence for the UK My Little Pony line. Although for most people in the world, the first adult boy ponies were the Adventure Boys (Big Brother Ponies), in the UK they had to take second place. Though some have suggested the Mountain Boys were part of 1988's line, there are a number of pieces of evidence to the contrary.
The First Adult Boy Ponies in the UK: 1987 release
MOUNTAIN BOY PONY CARD FRONT: 1987
First and foremost is the card style. The style of the Mountain Boy card matches the style of other cards from 1987, involving the rainbow in the design and without a border. The 1987 cards are some of the nicest UK release cards, and this one is no exception to the rule.
Another key piece of evidence is their appearance on the 1987 insert, and their inclusion in the Fact File seems to cement it. They were also sold with puffy stickers, for which the last year was the 1987 release. The Adventure Boy Ponies, though appearing on the 1987 second insert, actually appear to have been properly launched in 1988 and it they, not the Mountain Boys who were part of that year's line.
The Mountain Boy Ponies appeared in the UK comic in 1987, before the Adventure Boy Ponies did, and also appeared in the 1988 Annual, which went on sale in October/November 1987 in time for Christmas.
The final piece of evidence for me, though, is conclusive. That is the fact that I had Sunburst in November of 87, to mark the birth of my sister. According to my mother's recollections, she bought Sunburst in October, meaning they were out in the Autumn of that year. I had Fireball and Thundercloud both too as a kid, and as my birthday and Christmas are close together and not long after November, it seems probable that the Mountain Boys were out from the Autumn of 1987 to the Spring or Summer of 1988, where they were replaced by the Adventure Boy Ponies (and never returned).
Though there are similarities with the brushes and combs between this set and the Adventure Boy Ponies, these six ponies did not come with hats or bandanas. Much as any traditional pony of this time, they had brushes/combs, ribbons and a round puffy sticker. They used the same 'clydesdale' or Shire Horse style poses that the Brother ponies used - with two characters in each pose.
MOUNTAIN BOY PONIES: 1987 first UK Insert.
(It's worth noting that this insert has Lightning and Tornado named the wrong way around - but it's the only insert the set is on, so what can you do?)
While some collectors confuse Mountain Boys and Big Brother Ponies, they are far from the same thing. These six ponies are the ONLY adult boys to have white freckles on each cheek. They also had symbols based on elements and weather, rather than sports and hobbies that the Big Brother Ponies had. Somehow, a weather fixation is something only the British could dream up.
MOUNTAIN BOY PONIES: Hasbro UK Booklet 1987
(Thanks to Pranceatron for this image)
The six new boy ponies were introduced in the UK through a pony comic story (as most were at the time), called "There's Magic In Misty Mountain". It was a two part story, spanning over 2 comics. They were discovered by Baby Lucky, who till then was the only official boy pony in Ponyland. The entirety of this story can be found in the comic section of the MLP Media part of the site.
The Mountain Boy Ponies have only been confirmed as being sold in the UK and Scandinavia (where they were sold on UK cards). They were not sold in continental Europe, or North America, and their status in Australasia is still under debate.