Make an arena out of wooden platforms with multiple levels. Take down the Creepers with a Space Gun & Meteorite setup and if he teleports on you, grapple to a far away platform to free yourself. When one or two creepers are left on low HP, switch to Fossil Armour and chuck Bone Javelins into its head.
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Enjl
Enjl
In the second phase, while throwing these javelins, move away from him. Near the end it'll be hard to distinugish him, but you should have a healing potion ready so you get multiple shots at it. The damage over time from Bone Javelins really helps taking down this boss.
Drok
Ok how do i get fossil armor and bone javelins?
Enjl
Desert Fossil, then toss them into the Extractinator. You'll need a nightmare pickaxe so I suggest you die a bunch to the Brain of Cthulu while collecting some tissue samples. I'm assuming you have some Crimtane left from the Eye of Cthulu.
Drok
So it's found in the underground desert? That may be an issue 
Its like the size of a house.
Its like the size of a house.
Enjl
The underground desert is as large as the underground snow biome. Just dig a bit deeper. It took me ~600 Desert Fossil to get enough material for the set and a reasonable amount of Javelins.
Drok
@Mathijs99 sorry but no at least not for now i want to do this myself. @Enjl Mine is next the the snow and the snow took priority :P Still bigger than i thought but its just still small. Also is it an ore or just a random change from enemies, ect?