An IK rig for pony models. Compared to the other rigs I've seen, this offers better joint placement out of the box, so that your legs don't twist randomly. Perhaps more importantly, this rig uses aim constraints to extend the rig to cover that extra joint in the pony leg.
The script comes in two variants. One makes the toe (the hoof) the root of all leg movement, while the other makes the foot (the lower knee) the root. I prefer the former, as it is closer to the goal of a three bone IK. However, the rig prioritizes placement of the foot over the toe, so some may find the latter to be more natural.
1. Position the toe/finger.
2. Rotate the toe/finger OR position the foot/hand.
3. Position the toe aim/finger aim.
In step 1, position of the foot/hand is prioritized. This means that the hoof may not reach the desired location, even if it is within reach. Step 2 can solve this problem.
1. Position the foot/hand.
2. Rotate the foot/hand OR position the toe/finger.
3. Rotate the toe/finger OR position the toe aim/finger aim.
In step 2 of both rigs, rotation is preferred, as it maintains the correct distance between toe and foot nodes. This makes it easier to predict exactly where the hoof will end up.