When used, it kills all monsters on the board that are under KR, making it extremely similar to Patience's Snow Storm. In fact, aside from its +1 in cost and the obvious requirement of KR rather than Paralyze, it's exactly the same.
It's best used as a follow-up to Pollutant Gas, which will give KR to all enemy monsters that don't have it, resulting in a 10G enemy board wipe. Other options are single target ones like Poison, and Termination to a lesser extend, though quite wasteful.
Spiders (alongside Muffet's Pet) are also obtainable through Spider Web, making Perverance a good adition to a Muffet based PV deck. Worms, meanwhile, are also obtainable through Worming Up, though it's not so much a good 1 turn combo card due to its high price.
- Perishing Souls (by Diamaincrah)