I'm not entirely sure which 'Bowser' is specifically related to 'My Little Pony'. In the My Little Pony universe, there are many characters with their own unique backstories, but if this is a non - canon or very specific crossover idea, there isn't much known without more context.
There's not much official information about a 'Bowser' in My Little Pony. It could be a creative mash - up by fans. If so, a possible backstory could be that Bowser was a misfit in his original world and ended up in Equestria by mistake. He then has to adapt to the very different and friendly environment of the ponies.
Perhaps in this version, the ponies take on the roles that were originally in Bowser's inside story. They could be exploring a dark and mysterious place within Ponyville or some other magical land. They would need to use their unique pony powers to overcome obstacles, like Twilight Sparkle using her magic to solve puzzles and Rainbow Dash using her speed to escape from danger. It could also involve some sort of conflict between the ponies and an evil force that has invaded their special place.
Bowser's back story is quite complex. He was born into the Koopa race. As he grew, he witnessed the beauty and resources of the Mushroom Kingdom. This led to his envy and the ambition to make it his own. He has been in constant conflict with Mario, who stands in the way of his conquest. His upbringing in the Koopa Kingdom might have also influenced his aggressive and dominant nature.
One possible story could be that Winona, while on the back of one of the ponies, discovers a hidden path in Ponyville. They then embark on an adventure to find out where the path leads, perhaps to a long - lost magical place full of ancient pony artifacts.
One really funny moment was when Pinkie Pie tried to throw a surprise party for Rainbow Dash, but she kept accidentally giving away the surprise. Every time Rainbow Dash would turn around, Pinkie Pie would be in a crazy hiding spot like inside a flower pot or hanging from a tree branch, and she'd make a goofy face trying to stay hidden.
No. My Little Pony is typically known for themes of friendship, magic, and adventure. A breast expansion story goes against the family - friendly and positive nature of the franchise.
In My Little Pony, there could be instances like ponies excluding others from events in Ponyville. For example, if a new pony moves in and some of the more popular ponies don't invite her to the big gala. It's a form of social bullying.