Requirement to kill: 95 Slayer
How to get there:
Gear (Recommended):
Helmet: Void Ranger Helmet (With Elite Void Set and other parts)->Armadyl Helmet->Archer Helmet->Neitiznot Helmet
Top: Elite Void Top (With Elite Void Set and other parts)->Armadyl Chestplate->God D'hide Body->Black D'hide Body
Bottom: Elite Void Robe (With Elite Void Set and other parts)->Armadyl Chainskirt->God D'hide Chaps->Black D'hide Chaps
Gloves: Void Gloves (With Elite Void Set and other parts)->Barrows Gloves->Ranger Gloves
Cape: Assembler Max Cape->Ava's Assembler->Ava's Accumulator
Necklace: Eternal Glory->Necklace of Anguish->Amulet of Fury
Boots: Pegasian Boots->Ranger Boots
Ring: Archer's Ring(i)->Archer's Ring->Ring of Wealth (You can also equip row right before the kill, or just equip it all throughout)
Weapon: Twisted Bow->3rd Age Bow->Dark Bow
Arrow: Dragon Arrows->Amethyst Arrows->Rune Arrows
Prayer: or if you do not have rigour.
Inventory Setup:
All of which can be found on Consumable Store at ::shops.
The Kill:
Once you get to the entrance, , left click on the door and you will proceed inside.
Immediately rush over to the south-eastern most part of the lair:
and step on these tiles: so that you can lure the boss to the big red tile.
Once you have lured it properly, there will be a text on your chat box that says:
When you see this text, you may now begin to attack Alchemical Hydra.
Once Alchemical Hydra's HP gets below 825, it will change its form and become BLUE in color.
When this happens, you now need to lure it to the green colored big tile, which is just north of the red big tile.
To do that, you will need to stand on one of these tiles highlighted:
After successfully luring Alchemical Hydra, and waiting for the text on your chat box regarding its defense, you can continue hitting the boss until the next phase begins, which is when Hydra goes lower than 550 HP.
Do note however, that at Alchemical Hydra's blue phase, it has a special attack, which are blue lightnings on the ground that move towards you. Getting hit by one of these will stun you, and you cannot get out of place, which may lead to more lightnings hitting you.
The one highlighted in green shows what the lightning looks like before it hits the ground, and the one highlighted red is what it looks like when it is moving towards you.
Once Alchemical Hydra's HP goes below 550, it will change its color to RED.
At this point, you now need to lure it to the big blue colored tile, which is just west of the big green colored tile.
You can lure it to the big blue colored tile by going to one of these highlighted tiles:
Once again, after you see the text on the chat box regarding its defense, then you can again start attacking it.
On the RED phase, Alchemical Hydra has another special attack, which are flames that surround you, as well as follow you.
To avoid this, simply turn your run off when you start to see the flames, and just walk. This usually lasts for about 20-25 steps, after which you can continue hitting Alchemical Hydra. Keep in mind that you may trigger the flames the same time Alchemical Hydra switches phases, so to avoid confusion, you should be alert at all times.
Keep hitting Alchemical Hydra until its HP goes below 275, where it will change color again, this time to BLACK.
At this point, you don't have to lure it anymore, and just continue hitting it until it dies.
Bare in mid that after successfully killing it, don't go near its corpse right after it dies, as it still damages you.
To summarize, when you start your fight versus Alchemical Hydra, drink up on your ranging potion, as well as antidote. Lure it to the big red tile at its first phase, and continue hitting it until it changes to blue phase at, or below 825 HP. At the blue phase, remember to lure it to the green colored tile while keeping in mind the blue lightning special attack, and always try to avoid it. This is where your combo food (Karamb + shark/manta comes in handy). Keep hitting Alchemical Hydra until it changes to red phase at, or below 550 HP. Once it's at the red phase, lure it to the big blue colored tile, and keep in mind of the flame special attack. Hit it once again until it changes to black phase at 225 HP, wherein you do not have to lure it anymore, and kill it.
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Once you have gotten used to killing Alchemical Hydra, you can fasten up your kills a bit by moving while attacking Alchemical Hydra, going towards the next big colored tile, but not yet luring it since luring it to a wrong color will strengthen it. Here are highlighted tiles where you can step on so that you do not lure it right away, but you are already near the luring spot for the next phase.
That's about it, have a good day.
@Jordan