Invisibility might be a really great thing should the caster himself use it. However, should the caster's foes use it to make themselves and the possible loot invisible, then in can be really annoying. Dragons also love to turn themselves invisible and then roast their enemies.
However, all this is no problem with this spell. Casting it, all invisibilities in the area are dispelled, leaving the foe without this advantage.
Wis Quas strips illusion from creatures hidden by the cloak of invisibility, instantly revealing their position. Nightshade cut many times to form a paper-like sheet, then carved into lace is secured by spider silk. It is glazed, dried in the sun, then crystallized into a shiny powder that must be tossed in the sky over the field of battle as the spell is cast.