Radiant Ionic Spark

Reduces the target's Magic Resist (commonly by 30%, though the amount varies by source) for a duration, or for the rest of combat with some effects.

The unit-level resource that gates ability casts — champions cast once their mana bar fills, so low-mana units cast more often than high-mana ones. Spear of Shojin (mana per attack) and Adaptive Helm (amplifies Mana from all sources) push casts faster, alongside starting-mana augments.