So i actually got two questions about it and im not sure if i get it right:
Who moves Unkar Plutt:
my answer would be your opponent.
In which order are ships moved:
i would think initiative, first player moves all ships he can move, then second player.
If i am right with both, Unkar Plutt would be really really complicated to plan, as you need to think about a lot before you decide to try having him bump someone. Initiative, Angles from both manouvers....
If your opponent got initiative,depending on your angle he could or could not roll you on the asteroid you would want his Soontir to be sitting on and thus deny you a good tractor repositiong on his ship....
