Go there at /time 18, it will take a minute or two for the first spawn of Rilo or the ph young viper. After killing it wait 15 minutes for respawn. After killing twice in a night that's it, night lasts 30 minutes or 2.5min/hr so I'm like 99% sure it's impossible to get a third spawn.
Requires the following:
1 x Novice Tunic Basis
1 x Improved Cloth Cord
1 x Celestium Dust of Acuity
Makes the Burlap Elementalist's Tunic
Cloth Chest wearable by Everyone
7 AC +1 Intellect
Cave is very unforgiving. Bring an enchanter/CC. Spent couple hours in here and never saw anything drop. Lot of squeeze and no juice for me out of here. Corpse recovery's usually end up needing second group for backup.
Hobgoblins have been changed as of last patch to no longer be group (chevron) mobs. They still have some nasty abilities - shaman caster, and pressure point armor come to mind, but they are definitely doable solo now.