Big Bertha is obtained by defeating a variety of bosses found not only in the Overworld but also in other dimensions. It is crafted using 3 separately constructed items: The handle, the guard, and the blade. It does 500 attack damage, has 9000 durability, and has an extended reach. The way this is achieved is when you swing the sword, it will fire two invisible projectiles that do a fixed damage. Therefore a strength potion will not work at long distances, whereas within close proximity the regular sword hit will be amplified by the strength potion.
Crafting[]
Here is a list of the bosses and the pieces they drop for the 3 parts:
For the handle, you need to kill a Water Dragon for the Water Dragon Scale, a Mantis for the Mantis Claw, a Hercules Beetle for the Big Hammer, a Triffid to get the Green Goo, and a Robo Warrior for the Frickin' Ray Gun (or certain other mobs).
For the guard, you must find and kill an Emperor Scorpion to receive the Emperor Scorpion Scale, a Basilisk for the Basilisk Scale, a Nightmare for the Nightmare Scale, a Jumpy Bug for the Jumpy Bug Scale, a Mothra to get a Mothra Scale(s), a Molenoid for the Molenoid Nose, and a Sea Monster to get the Sea Monster Scale.
For the blade, you will need to kill a Sea Viper to get the Sea Viper Tongue, a CaterKiller Jaw from a CaterKiller, a Vortex Eye from a Vortex, a T-Rex Tooth from a T-Rex, a Worm tooth by killing a Large Worm, an Ultimate Sword, and a Kraken Tooth from defeating the Kraken.
Combine these 3 parts in a diagonal formation from bottom left to top right in your crafting grid to obtain Big Bertha. Combining Big Bertha and an iron ingot in a crafting table will allow you to create Slice (a white version of Big Bertha). There are no differences between Slice and Big Bertha, apart from appearance. The damage and enchantments are exactly the same. One won't be more use to someone than the other in battle.
