I used to do what I called a 'diamond braid' on my son's pony. You need a longish mane to do it. I don't have a decent picture to show you what I mean though.
I divided the mane with bands just as you would for an ordinary braid, so you end up with a whole heap of little pony tails.
Then I would split the first and second ponytail and join the two halves together and repeat for all the other ponytails.
Then, for the next 'row' I would repeat the process.
You end up with rows of diamond shapes.
It can look very effective.
This is the only photo I can find of it, not sure if it shows the plait good enough, but may give you a bit of an idea.
Only As Old As You Feel - Sometimes I Feel VERY Old