Board Thread:Help Board/@comment-27072805-20151027130946/@comment-24277289-20151028125108

Take it this way.

Pretend that Tridon's shield gives extra health to units (which it pretty much does.)  It gives a 3000 HP shield to everyone. If a unit has 9000 HP, it's HP + the shield = 12000. Now, if the unit has 50% mitigation, every 2 damage the enemy would normally have done will only do 1 damage. If the enemy was going to do 10000 damage, then your unit will only receive 5000 damage, which will destroy your shield and leave your unit slightly damaged.

The shield does not cancel mitigation, but can receive mitigation and take less damage, just like normal HP.