What changes to specific Witch Doctor skills can I make through equipment?
As per DiabloFans' list from the Bradygames Strategy guide:
Firebats - Reduced Mana Cost
Haunt - Boosted Damage
Poison Darts - Boosted Damage
Spirit Barrage - Boosted Damage
Plague of Toads - Boosted Damage
Corpsespiders -??? (Transcribed improperly)
Locust Swarm - +% crit chance
Firebomb - Reduced Mana Cost
Zombie Charger - Reduced Mana Cost
Wall of Zombies - Reduced Cooldown Time
Acid Cloud - +% crit chance
Summon Zombie Dogs - Reduced Cooldown Time.
Exact magnitude varies with level and the exact item. Most of these show up on Voodoomasks / Dolls / Ceremonial knives, but they can appear on regular helms, offhands, and weapons as well.
You can actually get a look at this by searching in the Auction House, as each skill modifier shows up as an individual search. Here's what I was able to find, along with the visible ranges for each effect (it's very likely that these aren't the caps, just that higher ones aren't posted):
One handed and two handed weapons:
- Reduces resource cost of Firebomb by X mana. (AH shows a range between 1 and 7.)
- Increases Haunt damage by X%. (AH shows a range between 5 and 9%.)
- Increases Plague of Toads damage by X%. (AH shows a range between 5 and 11%.)
Off-hands and two handed weapons:
- Increases Poison Dart damage by X%. (AH shows a range between 5 and 11%.)
- Increases Spirit Barrage damage by X%. (AH shows a range between 5 and 10%.)
- Reduces cooldown of Wall of Zombies by X seconds. (AH shows a range between 1 and 3.)
- Reduces resource cost of Zombie Charger by X mana. (AH shows a range between 3 and 9.)
Armor:
- Increases Critical Hit Chance of Acid Cloud by X%. (AH shows a range between 1 and 6%.)
- Reduces resource cost of Firebats by X mana. (AH shows a range between 1 and 9.)
- Reduces cooldown of Zombie Dogs by X seconds. (AH shows a range between 1 and 6.)