From The Bakugan Wiki
Add Core (Unofficial name) is a Combat keyword in the Bakugan Pro Trading Card Game. Bakugan with the Add Core symbol add a BakuCore from the Hide Matrix to itself when it opens and any prerequesite conditions are met. Nanogan with the Add Core symbol add a BakuCore to your active Bakugan on activation.
Cards with Add Core
This list contains a list of Bakugan, or their respective Evo, that contain an effect that features Add Core.