Tag Team Achievement
Used teamwork to perform a cross-class combo.
These combo attacks only require two of the three classes. Certain abilities will set your target up for a combo from the other two classes by staggering, disorienting or making the enemy brittle. These become much easier to perform at higher levels due to a wider range of abilities being available. You will most unlock this achievement without even knowing the combos and can be done by watching your companions fight.