Maybe a person should use thickish Jello? At least the shirts wouldn't be ruined...If you used enough colors the shirt might take on a marble effect!
How many more riders would it take to use your games? The max total I might be able to get is 5...But for sure 1-3...Pony included...
We were thinking of just getting some cheap tees from walmart or something. Thought it might make an interesting tiedye. I don't know if jello would stick to the end of the pool noodles.
5 people would probably be about the minimum for the other games
One of my favorite is musical cones (or musical pole/musical barrels/whatever). Just like musical chairs except on horse back. Obviously space the cones further apart than you do chairs. Everyone rides around on the rail and when the music stops you have to get to a cone and halt. If you aren't halted, it's not your cone! Last one left without a cone is out. And so on until there's a winner. This game requires someone on the ground to control the music and remove cones.
Another favorite of mine is called Herd the Cow. Do NOT play this with any horses that kick! You could probably play this one with just 4 or maybe even 3 people.
One person and their horse are designated the 'cow'. Everyone else are the herders. The 'cow' starts at one end of the ring. The 'cows' goal is to get to other end of the ring, while the herders try to prevent it from doing so. If/when the 'cow' reaches the other end of the arena, the game ends.
I also like Steal the Bacon. There are any number of ways you could set this up, but we always put a barrel in the middle of the arena. Then place the 'bacon' on top of the barrel, which is really just an object that would be reasonably easy to grab (ie. A hard brush, a tennis shoe, whatever).
Split your group into two teams and have each team assemble at opposite ends of the arena. This game also requires a neutral party, to call the shots or a referee as I will refer to it. Assign numbers to each team member.. if you were playing with six people. Team A would have a 1 person, a 2 person and a 3 person. Team B would also have person 1, person 2 and person 3.
Once everyone is lined up and ready, the referee would yell out something like 'Team A, 2; Team B, 1; ready, go!' So, person 2 from team A and person 1 from team B, go as fast as they can to the barrel and try to grab the 'bacon'. Once you have the bacon you have to get back to your teams side with it, to score a point. BUT if the person from the other team beats you back to your teams side, the point is negated. So if it's your turn and your opponent gets the bacon before you can, you want to try to get to their teams end of the arena before they can, to block them from getting the point. If someone goes when their number wasn't called, their team loses a point.
We've also played this game, where each team only had one horse, so when the numbers were called, the rider had to quickly mount up before running to get the bacon. This made it a bit more interesting/exciting/scary for those of us supervising. The teams had to work together to help each other mount. But you should only do this with really quiet horses and the players tend to get riled up.
And of course red light, green light is fun. Basically same rules as when you play on foot. But after the 'caller' yells red light, they count to 5 out loud, to give the riders time to get stopped, and then turn around. If anyone's horse moves once they've turned around that rider must go back to the start. The first rider to get close enough to tap the caller wins.
You can also play 'Ride the Buck'. We've always played bareback, but you could do it in a saddle too. All you do is place a dollar bill (or anything else that would work. We've also used poker chips which are a bit more difficult than dollar bills), place the object under the inside of each riders thigh, about halfway between knee and hip. The rider is NOT allowed to touch the object once it has been placed. The the riders are instructed to walk, trot, canter, reverse, post, sit, whatever. The rider who manages to keep their object under their thigh the longest wins!
That's about all I can think of at the moment, I'll try to remember some more later.