How do you easily defeat the mechanical bosses?

[Demon Master]

I have been getting quite frustrated. No matter what arena/fighting area I have, and no matter what equipment, I die almost instantly. What are your ways of dealing with them? I'm currently trying to kill the twins. I have an orchailium repeater with jester arrows as my main ranged weapon (I chose to go for the ranged class). For armour I have orchailium headgear (ranged), orchailium breastplate and cobalt leggings. My accessories are cobalt shield, spectre boots, hard shackle, regeneration band and some magma stone thing (cant remember). My arena is basically just a skybridge with a campfire in the middle.

On my last world I went for melee and had full adamantite armour with a savage beam sword, using my destroyer arena (I still failed miserably).

 

[Gotcha!]

Dodge, dodge and dodge.
In your defense, they are hard the first time you meet them. If you instantly die though then you're not doing enough dodging methinks.
Try to create titanium or adamantium armour first, so you have a decent defense. Titanium is definitely the best, but you'd have to be lucky ofcourse.

I don't see any wings in your setup. Fighting these without wings is suicide (or at least left to pros).

How high is your skybridge? If you're in or near space, your dodging speed will take an immense hit. Better fight near the ground.

Vs Twins/Skeletron:
Don't underestimate the Phoenix Blaster, especially with Crystal Bullets. The Clockwork Assault Rifle would be great to have as well.

Vs Destroyer:
Get a bow/repeater and use Unholy or Jester's Arrows. Line up your shots to maximize their penetration.

 

[Demon Master]

Yes I do really need to work on my dodging skills.

I had wings on my previous character/world, and also had full adamantite, so I might just give them to my current character.

My skybridge is quite close to the ground.

I don't have the phoenix blaster or CWAR. My ranged weapons are an orchailaium repeater, and minishark. I really need to upgrade that to the megashark.

For the twins, would it be worth building a series of layers of wooden platforms above the bridge?

 

[DaBomb]

Try to get the cross necklace. It's super useful, especially for the Destroyer. Using a repeater and jester's arrows should make short work of the Destroyer, just have a good pair of wings for dodging. Once the Destroyer is defeated, make a Megashark and use asphalt to build a skybridge. You can then kite the other two bosses pretty easily.

 

[Gotcha!]

For the twins, would it be worth building a series of layers of wooden platforms above the bridge?

In my opinion, yes. It gives you much more dodging flexibility, especially against the Destroyer.
Try to get the CWAR and Crystal bullets. In my opinion it'd be very useful against the Twins/Skeletron.
And really, get some wings. Any wings.