It's likely easiest to use an animation for each direction. To start, each of the 8 animations would only have keys on frame 0, they are used just to set the skeleton's pose. You'd do something like this:
1) Determine which of 8 directions to use based on the angle of the mouse location relative to the player.
2) Apply the animation for that direction and updateWorldTransform
.
3) Adjust bones to point at mouse (whether using IK or manually) and updateWorldTransform
again.
After you got that working, then maybe you could make the animations so (for example) frame 0 and 20 are just before the transition to the adjacent directions, and frame 10 is pointing directly at the direction. You could then interpolate based on the angle to the mouse to choosing a time for the direction animation, so you'd get smooth movement between the 8 directions over 360 degrees.
If you wanted you could get fancier and do it all in one animation, still interpolating to choose the animation time, just from a single animation. It would be slightly easier to animate that way and the code is about the same.