The Weakness spell has really gotten out of control in Dragonspyre. It doesn't matter the type of monster, almost all of them cast Weakness.
Not only is it very frustrating when our carefully built & buffed spells get weakened, it also causes battles to drag out to tedious lengths. The other day, after being hit by several Weakness spells in a row, I felt like just quitting the battle rather than dig my way out from under all of them.
Please consider reducing or removing this spell from at least some of the monsters decks. (But please don't replace it with Black Mantle...)
You may want to try a wand that is a different school than your primary school, that way you can remove the weakness without ruining your traps and blades. If you have a balance blade, wait until just before you cast the big spell to reduce the chance of having the big spell weakened.
Or if you have more than one type of blade up, it will counter the effects of the weakness because different types of blades will stack and get used on the same spell. At that point, it doesn't matter how many weaknesses are on you, only one weakness gets used per spell, so if you have one Balance Blade or Elemental Blade or Spirit Blade up your big spell will be safer. It might be worth the 1 pip cost for an Elemental or Spirit Blade to get the boost.