What this does, is when a projectile hits a player, that player's timescale gets cut in half (If timescale was normal, it would be 0.5, if timescale was two, it would be 1, etc.) for about 7 seconds (normal time). If the timescale is 0.2 nothing happens.
There would also be a Negative Timescale Beam that doubles the timescale for 7 seconds.
If you can script, I can supply a model. I'm working on one now:

