Rift Mob:Keeper Sentry  

Two Keeper Sentries will spawn when a Keeper Defense (turret or lifespring) around a Sourcewell is upgraded to Level 4. If they are killed but the Defense is still level 4 they will respawn.

They will attack any monster, Telaran or Planar, that enters their aggro range. They can be used, easily, to help defeat surrounding monsters by dragging the mob into their range.