My Little War Criminals. Clever Shot and Boomstick.
(Design notes and lore tidbits under the cut)
So to start with Ocelot, I firmly believe in the theory that most sentient races in the MLP world reproduce through magic instead of sex, so crossbreeds become entirely possible.
The being said, Ocelot is the result of a pony (The Joy) and an anthro cat (The Sorrow) having a child, thus the mix of cat traits and pony traits culminating in Equestria's most problematic stallion. I of course had to make him inspired by an actual ocelot and even gave him small whiskers on the joint of his back legs. He's a pegasus so he can do impressive aerial tricks with his guns and to silently stalk from up high.
Now for his cutiemark, I of course had to have the revolvers (which implies he earned his cutiemark by switching to revolvers thus his cutiemark was discovered because of Bibo's influence) but I also added teeth! To represent his eternal devotion symbolized in the ideas of hunger and consumption.
For Bibo, the most important fact right off the bat is that he's an earth pony. Earth ponies are generally seen as stockier and more adept for survival on the ground, which would include forests of course. I'd like to think that people underestimate Bibo at first because earth ponies are often seen as unable to keep up with unicorns and pegasi, but he's capable enough to more than make up for the lack of wings or magic. I wanted his tail to kind of match his mullet but I think during MGS3 it would be cut incredibly short. I wanted him to have kind of patches on his coat as a sort of "natural camouflage".
Onto his cutie mark! It's self explanatory I think. He earned it by killing The Boss and taking her title (meaning he would be a blank flank up until the end of MGS3). It represents his talent for war and duty, because regardless of his personal affiliations, he still finished his mission. It also in my mind kind of represents his misinterpretation of The Boss's will, the interpretation that led to the idea of constant warfare so soldiers never lost their purpose, in a sense he "killed" or "tainted" The Boss's original intentions when he took her life, represented by the blood-stained flowers.
Anyways that is it, they are toxic codependent pony yaoi and wanted war criminals.
Now for some silly headcanons for them.
Ocelot has the cat instinct of wanting to groom not only himself but the people he cares about, but since he only cares about Bibo he's the only one who gets this special treatment. It's more of an affection thing but sometimes a hygiene thing if Bibo has blood on his coat.
Ocelot actually has paws instead of hooves but keeps them covered.
Believe it or not horses will actually eat meat whenever the opportunity presents itself, so Bibo still hunts and eats random animals, sometimes he and Ocelot will go hunt fish (Ocelot is a kitty he loves fish).
Bibo is shorter than the average stallion despite being built like a draft horse.
Bibo thinks Nightmare Moon is still out there, he's also from Equestria (hence why he believes in Nightmare Moon) where as Ocelot is from a completely different region of the world.
That is all I have to offer, feel free to add your own headcanons to this post if you want.