Fistful of Energon wrote:dip bent part in boiling water for 10-20 seconds (or really hot water from the tap) then either reposition by hand or put in between book, then place in freezer for bout 15 mins.
I have read that this changes the chemicals in the plastic. I don't know if it's true.
Lodge it between some things that will hold it bent as far in the opposite direction for an hour or so (if it curves to the left, hold it bent to the right). When you release it, it will be bent in the other direction but will straighten after a while. If you leave him posed with the sword held horizontally and flat it will bend under its own weight.