The triangle attack is a special attack, that requires 3 units before the Sacred Stones and Path of Radiance, it traditonially required
3 units of the same class i.e 3 Falcon Knights, or 3 Knights.
In Sacred Stones it requires two Falcon Knights and a Wyvern knight. Also the effect of the Triangle atatck is slightly different, also the Wyvern
Knights pierce skill is used as well as the x3 damage(Critical Hit), reducing your enemies defence to 0 and inflicting the damage.
Conditions to activate the Triangle Attack
First you need 2 Falcon Knights and a Wyvern Knight
Next position the two Falcon Knights adjacent(next) to the enemy unit
Now attack the enemy with the Wyvern knight
The Triangle attack will now activate dealing x3 damage and reduce the enemy Defence to 0
A video is available to download showing how the triangle attack works.