The Black Stalker Tips

The Black Stalker is the final boss of The Underbog.

Static Charge: This ability does 750 nature damage per second for 10 seconds and is not dispellable. This effect is similar to the Treacherous Aura placed on players by the Omor the Unscarred in Hellfire Ramparts. As long as the party spreads out you can minimize the damage that this debuff causes to the party as a whole and the healer can usually heal the debuffed player and the tank through it.
Chain Lightning: This ability takes her three seconds to cast and hits the target for 2000. It then spreads to nearby players, with the damage falling by approximately half each time.
Levitate: This effect brings a player in the air and when it wears off, a debuff will come on (Suspension) which lasts 20 seconds. However, it is dispellable. Players with ranged attacks can still attack the boss in mid air.
Spore Strider (Heroic only): Throughout the fight, the Black Stalker will spawn sets of three ~5000 HP adds every 10-15 seconds that will cast 1000 nature damage lightning bolts at targets. These adds are immune to fear.

Stay spread out during the fight. Both the static charge and the chain lightning will quickly decimate your group if you stay bunched up.
The chain lightning has a 3 second cast time, so melee can watch for it and run out to avoid chaining it.
It is advisable to have on person dedicated to dispelling levitate so the debuff gets removed quickly. Levitated players can only cast instant-cast spells, and thus a levitated healer is severely crippled.
Mages may blink out of the levitate.