From my experience so far, Underbog is the easiest Heroic (compared with Ramparts and Blood Furnace). We found the following to be most sucessful.
Simple notes so I don’t forget. I believe these methods would work in non-heroic Underbog.
Hungerfen: Clear to the spiral up to the first boss. Also clear fully around the base of the spiral leading up to the first boss. Pull his two guards and kill them off.
Everyone should wait on the bridge from the spiral to the boss platform. Tank should run in and grab the boss. Tank the boss while walking him backwards down the spiral and then around the base of the spiral. This makes it so that mushrooms grow and burst behind the boss and away from the party and no one dies to spores.
I’d prefer to backwards walk the boss all the way to the instance door.. but that’s only possible if you’ve cleared out the first floor.
In theory you could tank him down the spiral, around the base of the spiral and then back up the spiral. At about the bottom of the spiral he will get roots around himself. Stop hitting him then as melee damage heals him. After the roots, resume tanking.
Ghaz’an: Clear to Ghaz’an. Everyone should wait on the platform where the last nagas were killed. Tank and healer run towards Ghaz’an. Healer stops half way across bridge (in range to heal if necessary).
Tank should pull Ghaz’an and walk him back down the bridge to the platform where the nagas where. Tank should have his back against the wall. Tank and spank.
Swamplord Musel’ek: Tank and spank. Have the whole party cluster near the tank. Bear charges randomly person furthest away. If you’re close he won’t charge. Focus on Musel’ek first. Then focus on the bear/druid.
The Black Stalker: Healers and ranged DPS should stuff themselves under mushrooms to avoid being levitated.
I’ve heard conflicting advise:
#1 3 adds will appear. Ignore them and focus on killing the boss.
#2 2 sets of 3 adds will appear. Kill them off and then kill the boss.
We did #2 but I’ve been told that if you do #1 and leave the adds alone, you only get three of them.