The problem probably is in the code. It's calling something, but it doesn't exist, which causes the program to crash. For example, you are probably sending p1, p2, p3, p4 to play on that stage (even if p3 and p4 are empty / null). The code for the stage takes in p1 and p2, but p3 and p4 are still being sent, causing a problem.
for example, using java code:
masterHandStage(p1, p2, p3, p4);
...
public static void main(Player p1, Player p2)
{
...
This would result in an error since the objects being sent do not match the objects being called. Namely, 4 are being sent, but two are being called, causing the program to crash.
I belive that is the initial problem we run into when we try to run that stage.
If we do solve that problem, we will get many more, like:
*starting animation and ending animation (master hand entrance / exit)
*p2 dies after losing his last stock
can't think of any more.
Thinking about it, I think the code for all the other stages and the one for the master hand are different, since they had different purposes. If it is possible to use another stage (like Polygon) and switch the stage with the Master Hand stage (without changing any of the code... other than the music), it should work.
Also, as mensioned earlier by someone else, only p1 and p2 are programmed in the stage. A spawn point for p3 and p4 would have to be created for the stage to work.