Weapon Coding Help - Impact Grenades

[Emperor S P O O N]

I'm creating a Doom mod with some map packs and, obviously, new weapons. One of which I'm in dire need of help in coding.

The weapon works as follows:

 

The weapon would be an type of impact grenade. When the grenade lands or hits something the grenade expands an AOE energy field, and any enemy that is caught in the field gets sucked into the center and is dealt constant damage. After about 5 seconds the grenade explodes, and, depending on how many enemies were drawn in and killed, the radius and damage of the explosion increases. So, for example, if it caught about 5 enemies in the field the explosion would be small, but if it caught 15 the explosion would be massive.

 

I've tried coding it myself, but it never seems to work and the ZDoom wiki doesn't seem to offer up any help. I'm not asking for someone to code it for me, but at the very least point me in the right direction or post a link to a wiki page I might have missed.