The nexus is a egg that attracts every type of monster the monsters try to get the egg because the egg can spawn all types of monster anyway, it is a mod (i think) and here are the steps to making the nexus- THE PHASE STONE- you will need: diamond (in its gem form), redstone (powder), lapis lazuli (in its gem form), and a crafting table now listen carefully put the diamond in the middle, redstone on the top and bottom of the diamond and lapis lazuli on both sides of the diamond, now you should get a phase stone which is wihte with some color, now don't worry it is not activated yet so not monsters with come!- THE NEXUS- you will need: redstone (powder), obsidion, phase stone, and a crafting table now put the obsidion in the middle then put the phase stone on top of the odsidon after put redstone on the bottom of obsidion then put redstone to both sides of the obsidion, it should come out being a black square and andsome color bleeding through it on the sides and dont worry it has not activated yet!!- NEXUS CATALYST-you will need: redstone(powder), flesh, bone, bowl, and a crafting table, now remeber this is what activates the nexus, now you put the redstone in the middle then put the bowl on the bottom of the redstone then put the flesh to the right onf the redstone and put the bone to the left side of the redstone.when you are done making that it should look sorta like pink powder anyways, take the Nexus and place it somewhere you can protect it-get ready to fight! then take the catalyst and right click the Nexus with it then it will start to activate slowly. Get ready to fight!