“A Magnus is created by extracting the Magna Essence of an object from its physical property... ...and sealing it in a card.”
- Man in Cebalrai.
In the world of the Baten Kaitos series, there are items called Magnus that can absorb the essence of almost anything, including weapons, magic, and items. The games are marked by a unique card-based system. Magnus cards can absorb the "Magna essence" of real-world objects for storage and later use. All objects have "Magna essence" which sustain their existance, even living people. It is rumoured, however, that live entities may not be stored within Magnus. There are five varieties of Magnus: Quest Magnus, Camp Magnus, Battle Magnus, Class-Up Magnus and Equipment Magnus.
Some Magnus may change over time, gaining a stronger, weaker, or all together different effect (i.e. a healing Magnus may rot and turn into a damaging Magnus). In effect, this means that deck management plays an important role in the world of Baten Kaitos.
Magnus can also be combined during battle. When certain Magnus are played (sometimes it must be in a specific order), Special (SP) combos are formed, thus creating a new Magnus. When an SP combo is performed, it will be listed in the "SP Combos" section of the menu. Some Magnus can only be found through the use of SP Combos. For example, Sacred Wine is formed by combining the Holy Grail and Sacred Wine or Holy Grail and Japanese Rice Wine Magnus. No other Magnus beside the required ones can be used when forming an SP combo.
There are seven types of damage: Physical, Light, Dark, Water, Fire, Wind, and Chrono. Each of the elements has an opposite: Wind vs. Chrono, Water vs. Fire, and Light vs. Dark. Every enemy is aligned with at least one element. Damage of the element(s) an enemy is aligned with will be reduced, and damage of the opposite element(s) will be increased. Using two opposite elements in the same turn will cause their damage to cancel. For example, if a player uses both a wind and chrono magnus, and deals 40 chrono damage and 60 wind damage, then they will cancel to 20 wind damage. Magnus aligned with an element generally deal some physical damage as well - for example, a Fire Burst Lv 1 deals 10 Fire damage and 5 Physical damage.