Sigilyph

Sigilyph can function as an offensive Defogger that can threaten Nidoqueen, Roserade, Metagross, and Registeel with its combination of Psychic and Heat Wave or a powerful wallbreaker with Calm Mind. Magic Guard prevents damage from Stealth Rock, Life Orb, and status, allowing Sigilyph to avoid chip damage and use Defog or set up more consistently. However, Sigilyph is largely outclassed by other hazard control options such as Mandibuzz, Mega Blastoise, and Donphan, which can check a lot of threats due to their superior bulk or offer better offensive presence. Because Sigilyph's Speed stat is only decent for an offensive Pokemon, it will struggle to revenge kill faster threats such as Shaymin, Virizion, and Salazzle. Bad defensive typing and bulk also leave it weak to common threats like Tyrantrum and susceptible to coverage moves found on Pokemon like Donphan, Virizion, and Mega Blastoise. Vulnerability to Pursuit from Pokémon like Drapion is another factor that makes it more unreliable. The prevalence of defensive Pokemon such as Mandibuzz, Milotic, and Porygon2 is a big problem, since Sigilyph can't beat them reliably with its STAB moves if not running Calm Mind.