Monsters, by living in their environment and by genetics, can grow attached to an element, which will then become their defensive element. Adventurers, in other hand, uses cards to enhance special magical weapons, to grant an offensive element. The right combination of offensive vs defensive element can be deadly, but not few adventurers lost their life for using the wrong element.
The main elements in the mana world are:
The neutral property underlies the whole world. Everything is neutral until they grow affinity for an element.
Fire burns, sending nature to ashes. However, one only needs water to shut off the fire.
Water is flexible, and extinguishes fire with relative ease. However, the nature can quickly absorb the water, neutralizing its effects.
Nature is the mother of all life, and it can reduce water to a pile of mud. However, fire can put an end to it.
The sacred element of things holy (or "Light"), largely used by priests, to purge darkness creatures. However, darkness is also their weakness.
Darkness (or Shadow) is cursed, used by undead to scare holy creatures. However, holy is also their weakness.