chris is right.
you can have the Player muleaccount; definition at the top, but you can't have any references to Script before onStart(), so you need to put the assignment in onStart()
your onStart() should look like this:
public void onStart() throws InterruptedException {
startTime = System.currentTimeMillis();
muleAccount = getPlayers(...);
log("Welcome to beef slave");
log("This is a quick money making method");
log("Please post errors to thread");
}