Do you mean a random chooser that determines whether they will hit with their main hand, or off hand? If so, that is rather easy, especially with a variable.
Firstly you need to make a variable and call it "Hit chooser"
Secondly, at the event in which your character punches, you need to choose a variable operation.
Make sure the variable being changed is the "Hit Chooser".
-Make sure the Variable operation is set to "Set Equal"
-Make sure the Operand is set to Random "Number Between"
-Set the first number in the box to 1, and the second on the box to 2
After that is done, you need to make a conditional branch.
-Make sure the Variable circle is ticked, and following that, the variable "Hit Chooser" is selected.
-Type the number in the box as 1, and the value to EQUAL TO.
-Un-tick the "Execute Custom Handler If Condition Not Met" box.
-Press Ok.
Make a new conditional branch exactly as the above, but this time set the number of the variable in the box as 2.
Your event for the punch would be like this verbally:
When you press the button, it will proceed to the "random chooser" section, which will then choose a random number in the range it was given--In this case it was 1 and 2.--and it will go either way. Because this is a two choice way. It will either be 1, or 2, you can set which direction under the IFs in the conditional branches.
You also want to remember that there is 4 ways your character can face. So to solve this, you need to make a conditional branch in the conditional branch which says:
"Conditional Branch is Var [XXXX: Hit chooser] Is X"
Under that, you need to put a conditional branch which checks the players direction. this is easily found under the conditional branch page on Tab 2.
Sprite: Hero is facing: Up.
-You need to change the graphic direction to the facing up direction. and repeat the above for every direction.
For the sake of confusion, here is an example of what I mean.