And how would I do that exactly?
You would have to create a random number generator (RNG). The method that I typically use is as follows (with modifications to fit with your thing):
[0] [x] [0] [OnActivate] [Self] [VCE_ModVariable] [NumberVariable] [Random]
[1] [x] [0] [OnActivate] [Self] [FireRelay]
[2] [x] [1000] [OnRelay] [Self] [FireRelay]
[3] [x] [0] [OnRelay] [Self] [VCE_IfVariable] [NumberVariable] [<] [.5] [4 5]
[4] [x] [0] [OnVariableTrue] [NamedBrick] [Projectile1] [SpawnProjectile] [Pong] [1]
[5] [X] [0] [OnVariableFalse] [NameBrick] [Projectile2] [SpawnProjectile] [Pong] [1]
Projectile1 and
Projectile2 are the bricks that you used to spawn the pong projectiles.
NumberVariable is just a variable, what it says in that box must match with what you put before. This would cause a projectile to spawn once per second. I saw that the time between projectiles decreased in increments over time, so you'd have to include that in the RNG.
[edit]
Also, this system was only for two projectile bricks. If you want to add more, you'd have to add more ranges in variable checking to account for all possible numbers generated.
