Tips to update your game:
1. select the background of the buildings, right-click and press selection>move selected to back (so that the zombie tracer dosen't get hidden)
2.learn part 3 and 4 of the series as fast as you can. It contains the if-statements(part 3) and other stuff like weapons, medkits, etc(part 4) which are necessary for the life of the marbles and zombies to go and for them to attack.