Thats just evil
1. The wall can take exactly 12 hits (the wall has 100hp and each person does 9 damage when they crash into it and die).
2. One, ONE, person makes it through and GAME OVER.
3. Repairing the costs 500 xp and each person you kill gives you 15...hmm, thats 34 people you need to kill.
4. I can kill about 5 people before 1 gets through.
I challenge everyone here to get 3 upgrades! (upgrades are 750 xp)