Combos happen when three of the same element are played in a row or if all four elements are played in a row (Aetheron). Both monsters and players can get combos. Once an elemental combo is achieved all of that element is removed from the board and the table is checked for further combos, if one is strategic enough they could get multiple combos using a single card.
The affects of the combos are:
Earth: Heal and receive defence bonus
Fire: Deal damage to opponent
Air: Recover energy and recieve attack boost
Aetheron: Gain energy, heal, gain attack, gain defence and deal damage