Checklist before doing Wall of Flesh? (Master Mode)

[H. P. Hatecraft]

I mean I don't want to haphazardly send my game spiraling out of control since I'm on Master Mode... it's already hard. I imagine it's extra hard once hardmode is enabled.

[GladiatorDragon]

I don't quite know much about Master mode, but I do have some recommendations:

Dig various tunnels from the surface to the Underworld that are at least 3 blocks wide, though I'd recommend making them 6 blocks wide just to be safe. It's a good idea to place them on the border between biomes, as the Evil biome of your world and the Hallow will spread like nobody's business once hardmode's active. It's a good idea to do your best to try to section them off. It's also not a bad idea to dig 3-block wide lateral tunnels across the world to contain the Underground Corruption/Crimson/Hallow. When Hardmode initiates, there is one initial burst of Evil and Hallow, and it ignores already placed constrictions. For this reason, you need to constrain it as much as possible, if you don't want it threatening your bases, or, arguably more importantly, the Jungle.

Try to get the best gear available. I don't know which weapon focus you're taking, so I'll list the best options here:
General: Crimson Armor doesn't focus on benefiting any weapon type in particular, and is a solid option, though it requires you to have a Crimson world.

Melee: Shadow/Molten Armor provide potent buffs to Melee weapons. Molten is overall better than Shadow, but you can use Shadow if you don't want to farm all the required Heckstone, if you have a Corruption world.

Ranged: Necro Armor is the best Ranged focused armor pre-hardmode.

Magic: If you want to take a hit to potential damage for infinite ammo, use Meteor for the infinite Space Gun. If you want to use more spells than just the Space Gun, use Ancient Cobalt/Jungle (which are considered part of the same set, and are interchangeable).

Summon: For summons, you'll either want Obsidian Armor or Bee Armor, whichever you prefer, alongside the Imp Staff.

As for other equipment,

Generally, it's a good idea to obtain the best mobility gear available to you. If you can obtain Fledgling Wings, that is an excellent start, but they are difficult to get. You'll want Lightning Boots (Hermes Boots + Rocket Boots + Anklet of the Wind + Aglet), or any of its crafting results (Frostspark/Terraspark) and the Lucky Horseshoe (or any of its crafted variants. Ignore if you have Fledgling Wings, which already negate fall damage). It's also a generally good idea to build a platform bridge in the Underworld that reaches from one side of the world to the other.

I don't really know enough about Master Mode (or really, this game) to help you more. Sorry if this is stuff you already know.

[geordiebroon58]

honistly the hardest part of any dificulty is

begining of a new world

begining hardmode

doing the soler piller as summoner without the terraprisma