Sunder Earth is a great AoE attack that deals heavy damage to all enemies standing in front of the caster snaring them. If the target is knocked down it will receive extra damage. Allies in front of the caster receive special debuff that decrease taken damage.
As you see it’s a great skill because of massive snaring effect. You can use Whirlwind Slash ability after Sunder Earth in order to benefit from knocking down combo. Whirlwind Slash will knock down all snared targets.
List of abilities that can be used in one combo attack before Sunder Earth