Opposed Powers
Certain magical energies oppose the effects of other magical energies. When the energies of two conflicting abilities come into contact, an Opposed Potency check is made to determine the outcome. Whichever ability wins the potency check persists, while the opposing ability is dispelled (or has no effect).
For example, suppose a Ray of Frost spell targets a Flaming Sphere spell. Since abilities with the Fire keyword are opposed by abilities with the Cold keyword, an opposed Potency check is made. If the potency of the Ray of Frost meets or exceeds the potency of the Flaming Sphere, the Flaming Sphere is dispelled. If the potency of the Flaming Sphere exceeds the potency of the Ray of Frost, there is no effect (at least for this target of the Ray of Frost spell, other targets may be affected as normal).
Certain power keywords oppose all abilities of another keyword, such as Fire opposing Cold or Light opposing Darkness. Alternatively a specific power can oppose another power or keyword, such as Deity's Boon opposing Deity's Curse or Silence opposing Sonic abilities.