make scalling for all mobs  thats over 300 ap zones  copy paste from Tron and liberty or warcraft they did very simple

1 person hit target it appear 1 star hp same 

2 person hit 2 star and hp of mob got double and in its hp bar go double 

3 person hit hp go triple 

 For some reason if 1 stop dpsing for 30 sec his chance for loot disapear and mob scale down so this canot be abused, but players that have friends and like to grind together can do it anywere