Nexus is a card type in the game Battle Spirits. They share traits of both Spirit and Magic cards. Like Spirits, they can be levelled up, have symbols, and remain on the field until depleted or destroyed. Like Magic, they cannot be used for battle, but simply to provide support.
Q1. Can core not be put on Nexuses?
A1. No, you do not need to put core on them, since normally Nexuses have a Level 1 cost of 0. However, if their Level 1 cost is 1 or more, core must be put on them equal to or greater than their Level 1 cost, otherwise they will go to Level 0 and be depleted.
Q2. Can any number of Nexuses be deployed on your field?
A2. Yes, there is no limit to the number of nexuses that can be on field.
Q3. When multiple Nexuses are deployed on the field, do their effects activate at the same time?
A3. Effects never activate at the same time. If there are effects of the same timing going to activate, they activate simultaneously, with the turn player choosing the order. Nexuses with same effects can all activate, unless it is stated "cannot be duplicated" or similar wordings.
Please refer to Grandwalker Nexus.