'HMWCYD?' means 'How Many Ways Can You Die?'. It's actually a test map which shows some neat ways to kill players. There's some pressure chamber, meat row, fridge, water, shrinker sparks etc. So when a player enters some room you close him there and watch him dying in different ways. This works best with just yourself because it's difficult to make bots enter these traps. And you won't get any points for killing someone with a trap. So it doesn't really work with dukematch. Just download this to see what you can do with Build.