Whilst the server is in HM, I thought that I would play single player to gather the resources and compete against the bosses myself (never actually done this before). I have killed the Eye of Cthulu and also dug my way down to Hell. I am fully kitted in Platinum armour, but that is still a little weak in Hell. Where do I go from here? should I try to find the Sky island? Or do I look for the Corrupted Land and fight the corruption? I have also made a Slime Crown, so that is my next big fight
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Definitely go to the corruption, the new armor you can get from farming the boss there a few times is a step up from platinum. It has more armor than the platinum set IIRC as well as a 4%(?) damage bonus and an increased health regen passive. Its the best all rounder armor you can get before HM. If you don't already know, the boss is easy enough to summon, you just have to destroy 3 orbs/hearts which are located in the corruption walls. To get to them you will need to use purification powder on the stone first and then mine through it.
If you've not been to the dungeon yet its also worth going there, the handgun you can find in chests can be crafted with molten bars into the best ranged weapon before hard mode(yes, the star cannons stronger, but who has an infinite supply of stars?). The muramasa is also worth finding as it can be crafted into the Nights Edge(?) which is the strongest melee weapon before HM. A cobalt shield will also come in handy, it shouldn't be too hard to find in the chests there. Last of all a shadow key can also be found in the chests there, it will allow you to open shadow chests in hell.
As for additional accessories/weapons you should have before you go into hard mode.
A red balloon from the sky islands, the islands are easy to find with a few gravity potions. Put the map so its full screen but transparent to easily keep at the right height while you search so you're not in danger of killing yourself.
An anklet of the wind and aglet which can be combined with other accessories like Hermes boots, the aglet should be easy to get a hold of but the anklet will be in the jungle somewhere.
Hermes boots, which can allow you to sprint, they can also be found in the jungle.
Goblin rocket boots are also worth picking up until you can craft wings, you can buy them from the goblin vendor or hope for a lucky drop during a goblin invasion
There's probably some stuff I missed out but I'm sure someone else can fill you in