Halitostrooper

How do you kill the Halitostroopers for the quest "Doing the Dirty Work? The always seem to run away and heal.

Stop pulling them so far from their spawn point.

Just pull them a little ways away, zoom your camera out and stay close to them. Whenever they use Putrid Breath run to your right or left immediately. It's a cone-shaped attack, so the closer you are to them the less distance it'll take to get away.

Don't forget also to immediately use the key item on the ugly plant that you're given as part of the quest, as this will greatly reduce their defense and strength, making them a lot easier to fight. But it really comes down to just avoiding Bad Breath (like all malboros) - it's a conal attack so you can rather easily dodge it (or else hit the mob with a stun attack like Shield Bash or Fluid Aura).