[quote=Tyki]
corpus is a mix of different things basically resulting flesh but corpus sounds cooler and they're my fucking elements -_-
[/quote]

However, your opposites are absolutely nonsensical. If you made a shield of earth, lightning attacks would have no problems piercing it. In fact, earth is a better conductor than air is. Air is a notoriously bad conductor. If you create a shield of matter, it's not going to stop time attacks. A shield of fire will not stop wooden arrows, simply turn them into flaming wooden arrows, which means it'll be even more painful when they hit you. A shield of ice will be molten and pierced by lava, and a shield of darkness is useless to defend against light. The problem is the difference between opposite, and what offers the best defense.
When facing light attacks, I'd use a mirror. Darkness is pretty much cancelled out by light, and not at all a useful defense. What one would think to be the opposite is quite often useless when defending against attacks of that element. if we're saying that you can manipulate elements, then you should be either using the same element to nullify it, or using the element that offers the best protection from said element. For example, electricity cannot travel in a vacuum, and thus a lightning attack, no matter how strong, will be blocked by a vacuum.