You need to start breaking Demon or Crimson Altars with the Pwnhammer. This will spawn three new tiers of ores that you need to mine. The ore you get is determined at random when you smash an altar. The ores are: Cobalt/Palladium, Mithril/Orichalcum, and Adamantite/Titanium. Each altar smashed will spawn some of the next ore in the list, starting at the few new tier. The first spawns Cobalt (or Palladium), the second Mithril or Orichalcum, the third Adamantite or Titanium, then fourth circles back around (Cobalt or Palladium). After each ore is spawned once successive altar smashes will produce less and less of that ore. And each alter smashed will spawn a block of Corruption, Crimson or Hallow somewhere in the world which will contribute to the spread of those biomes. I have heard it suggested that the new ores are more likely to spawn in the underground jungle, but I cannot verify this from my own experience.
Now, I personally like to aim for Excalibur and the Megashark first. That's because you need souls of Might - dropped by Destroyer - to make them. I find him the easiest Hardmode boss to tackle. Because of that, I don't build a lot of hardmode gear (except armor). I only need the swords (I go back and build other stuff later of course). But before I worry about swords or armor, I go for the drills.
It looks something like this:
Mine enough cobalt for a drill then mirror out and make it.
Return to mine for Mithril. Mine enough for the Anvil and a Drill, then mirror out and make those. I will mine cobalt during this trip down, and if I have enough spare I will make a sword (since you can hold it down and swing it, a property the Mithril and Adamantite swords do not share), then armor pieces.
Return and mine for Adamantite and Mithril primarily. Make Adamantite Forge, then drill (though this is not strictly speaking necessary, but it is an upgrade), then make Adamantite armor. Then make Adamantite sword. I will use Mithril armor as a stop gap until I get a full adamantite set.
During this process, you want to farm crystals when you can (if you plan on using guns at all; crystal ammo is amazing) and get as many souls of light/night as possible (can drop from any enemy killed in the underground Hallow/Corruption). Those souls are the gateway item for summoning the new bosses.
Once I can summon the Destroyer, I get a weapon to kill it with. Typically that's a Phasesaber. I make Excalibur (which really speeds up farming him) then I make the Megashark (which I use for the Twins and Skeletron Prime).
My way is not the "best" way, but I find the Destroyer easiest and I rather like those two weapons.Bow lovers can easily substitute repeaters for this process, and you can kill the Destroyer for a Megashark or just try to farm the twins (for the Hallowed Repeater) first. Magic lovers want to forge Crystal Storm.
There are a lot of options. My general advice is not to stop and build a full set of armor/gear at each new metal tier. Build as little as you need to progress to the mining of the next tier. If you are dying a lot, then alter tactics (and if need be, do stop and make some better armor).
Once you kill all of the Mechanical Bosses, the Hard Mode Jungle awaits!
The Corruption/Crimson spreads much more easily in Hardmode, with the Hallow spreading in a similar fashion.
- Corruption, Crimson and Hallow will spread to stone, sand, ice and dirt that are up to three tiles away.
- Almost all other blocks are immune to Corruption and Hallow, including Wood, Clay Blocks, Ash Blocks, Silt Blocks, Obsidian, Ores, Gems, and all bricks (except Pearlstone, which will spread Hallow).
- Corruption and Crimson can convert mud blocks into dirt over time. Mud blocks containing mushroom grass are not affected.
- Sunflowers will no longer prevent the spread of corruption. Instead, they will pop out of the ground as corruption spreads past.
- Hallow and Corruption cannot convert each other.
There are no longer enemies that spread corruption, crimson, or hallow. So, what you need is a 4 tile barrier made of pretty much anything besides stone, sand, ice or dirt. The favored method is by making a quarantine tunnel all the way around you base. My preferred method is as follows:
Start with a 4 block wide tunnel. You can use the Ruler if you're super paranoid.
While that tunnel itself is perfectly fine for hardmode protection, I like to line my tunnels with Some type of brick. This has multiple advantages such as thorns no growing in your tunnel (since the corruption can't spread over the bricks themselves), it looks nice and clean, and most importantly, it is a visual reminder to you and other players not to build there. Keep in mind that these bricks are in addition to the 4 air tiles
Now just continue with this tunnel all around you base. Give yourself plenty of room so you can keep your farms within the quarantine zone and so you don't have those hardmode enemies spawning right at you doorstep.
Best Answer
There is no standard order to kill bosses.
It depends on your armor, weaponry and (by my own experience) Mythril Armor is needed for any of them.
It's probably the best to do it like this:
It's recommended to have a good piercing weapon for Destroyer.
The Destroyer strategies page would help you.
After killing The Destroyer, you can kill The Twins very easily by using the The Megashark.
But Skeleton Prime is different from others. Hallowed armor is recommended to defeat it.