I seriously don't like the necromancer's degeneration aura . It deals damage to enemies , but if it kills your enemy , you don't get the bounty . Good one isn't that hard to make , especially when it's not MUI
The Nerco's aura is really used for its slow effect on the bad guys rather than the -regen, though a player with micro or use of Omnidrain can easily kill muliptle targets at once on very low hp without the aura claiming them first. Besides an instant drop-dead cash magnet would be a tad unfair with no player input required.