Hydra may have received some nerfs post Season 9, however with Ophidian Iris is able to be taken on a defensive slot as a Chaos Unique. You can farm this from Infernal Hordes by killing Bartuk. You can also do helltides and find Chaos Rifts that award Chaos Armor.
You can also farm it from NM dungeons with the Chaos Rift affix. You will need to scope your mini map for Legendary Chaos Rifts.
Lastly, you can turn in excess Seasonal Warp next to the Seasonal Board in Yelesna, which is located in the bottom right of Fractured Peaks. Every rank up past max rank will award a cache that contains a random Chaos Armor.
Hydra can use the Mana shield seasonal power to be practically invincible. It uses Power Siphon to double it's damage. It uses Mana Infused Conjurations for 30% more damage. Lastly it uses Alternating Alterations to increase it's damage by 60% after casting another core skill, which will either be Blizzard, or Blizzard and Ice Shards in the Pit Push setup.
The Serpentine Aspect is Hydra's strongest aspect. Typically it consumes all your Mana Shield when you cast it, but with Alternating Alterations it will only consume half your mana. The loop here is you cast Wizard Blizzard's to initiate a massive amount of mana regen, as it grants 1 mana regeneration per 20 max mana. The Mana Shield Seasonal Power will grant us upwards of 15,000 Max Mana which means we get 750 mana regen per second. If you happen to cast Blizzard after not taking damage for 2 seconds, this value will get increased by 5000%. It's actually insane and busted. Enjoy.
For Pit Pushing you can either do Direct Damage with ice Shards, or you can do Burn Damage with Firebolt. The Burn setup takes the edge, but in Pit Pushing alone. The Critical Strike Direct Damage setups perform better in all other content due to the immediacy of damage, as opposed to Burn which requires time to stack up it's damage over time. Pit Pushing consists of very tanky mobs that take a while to die, which allows Burn the time necessary to fully ramp up and get cooking.
Locran's Talisman? (No workie)
Locran's damage buff appears to not work with Hydra, crit chance might. Spaghetti Code
Elixir/Incense
Elixir - Advantage II for 15% attack speed
Incense 1 - Spiral Morning for 60 all stats for paragon reqs
Incense 2 - Song of the Mountain for 300 armor
Incense 3 - Soothing Spices for all resistance, max all resistance, and some armor