Here's one way to use nested rules in Kodu. In this example, rules 3 and 4 won't run unless rule 2 is true. What we're doing here is using score to keep track of ammo. When the user presses the trigger, we check the score. If it's above zero, we shoot. If it's zero, we play a sad...
There are two help systems inside Kodu that may not jump out at you but are quite handy, and will get handier over time. The first is the character help, which inserts basic preprogrammed characters into your world. It's triggered from the menu where you insert characters, below. Note the "Y"...
Here's a level I'm working on today which is an retro invaders / galaxian sort of thing: good guy moving back and forth at the bottom of the screen, bad guys diving from above. I had a problem where some of the more aggressive enemies could get down to my height and then ram my defenseless sides...
When you see a red blimp, move away (from it) See is a sensor, red and blimp are filters, move is a verb, and away is a modifier. UPDATE: corrected error in above line