Minecraft wiki entry for Half_hearted_hardcore, associated text: Make sure your armour, sword and tools are all netherite and maxed out enchanted, and you have a bow with Infinity, Unbreaking 3 and Power 5. Armour will need Protection 4, Unbreaking 3, Mending and optionally Thorns 3, plus Feather Falling 4 for the boots, the sword will need Sharpness 5 and Mending and the pickaxe will need Efficiency 5, Mending and Silk Touch (for ender chest usage).
Also make sure you wear a carved pumpkin to stop endermen from attacking you if you look at them. You can use a texture pack to get rid of the part that blocks your vision.
Bring at least six potions of Strength 2 and six extended slow falling potions. You have a chance to get a phantom membrane when you wake up in the morning if a cat curls up and sleeps on a bed with you. Night vision can help you see the dragon in the dark, and speed and gapples will come useful in the fight too!
Optionally, you can bring a trident enchanted with Riptide 3 and Mending, if you have enough slow falling potions or water bucket MLG experience. This will allow you to zoom through the air and will really help in accessing the caged crystals.
Also bring 2 buckets of water (to make an infinite water source) and at least 2 buckets of powder snow to tower up to the top of caged crystals.
Bring some ender pearls but only use them if you are knocked into the void. Slow falling will give you more time to throw them.
Do your best to bring as many totems of undyings as you can to a fight. It might save your life.
Make sure to utilise ender chest storage as much as you can. It will really help you carry all the potions!
Bring an enchanted golden apple or two if things go south during the fight.
Bring a single arrow for the Infinity bow and use it to destroy most crystals and also shoot the dragon in the air. For caged crystals the best way to destroy them is to get close and shoot through the gaps‌[JE only], but if you have bad aim or play on Bedrock Edition, you can ignite a piece of TNT on the top of the iron bars and use a Riptide trident or a water bucket to swim down before the TNT explodes the end crystal.