I have a character with a running forward and a running right animation.
When I mirror it to run left it doesn’t look quite right when blending between two points in the blend tree. He does an awkward sort of hop for the mirrored animation while it’s fine for the original one.
I tried tinkering with the settings in the animation import window but it didn’t help.
Well, usually when blending between two animation to make a smooth transition you also need a middle state: an animation in wich the character turns.
Now I am not exactly sure that your problem is with the lack of middle animation. You provided too few details. We will need some visual information.
I made a video here showing the problem at the end:
https://www.youtube.com/watch?v=011JHcI2aOY
The settings image.
It looks like your cycle offset is off.
The cycle offset is used to synchronize animations in a blend tree together.
For example, if your run and run right animations start with the right foot down, and your turn left animation starts with your left foot down, you need a cycle offset of 0.5 (so the right foot is down at the start of the loop)