Bolty's Note: Why didn't people use Hydra more?  It WAS a level 30 skill, and yet it was shunned by many Sorceresses prior to version 1.07 of Diablo II.  Here's the explanation.

Yet another potentially viable spell ruined by Blizzard programmers' oversight. The damage shown on the skill description is incorrect if you have any points in Fire Mastery. Just factor out the extra Fire Mastery damage to get the real damage, or look at what your Hydra damage should be at Chaos Sanctuary.

Why does this happen? Well, I think that because Hydra (it's a summoned monster) doesn't have any points in a skill called Fire Mastery, it won't do more damage with it's fire bolts. Fire mastery only increases fire damage that you do directly.

I also heard some rumors on D2SF that Hydra rate of fire increases with skill level. This is NOT true. Hydras seem to average a firebolt every 0.4 to 0.45 seconds, regardless of skill level.

I don't keep up with sorceress news much, so hopefully all of this hasn't been said before.

Bolty's Note: This bug was corrected in Diablo II v1.07.