Stuck on a birthday cake...

Hey everyone, I need some help. My step-son has requested a VW Bug, Zombie apocalypse cake for his 12th birthday here in about two weeks. Problem is he doesn’t even know how he wants it to work and I am beyond clueless. Does anyone have even the slightest idea on how I could do this? The party will be for about 20-30 people roughly. Any help would be greatly appreciated.

Thanks!