Dialga

Dialga is a great lead because it sets Stealth Rock reliably thanks to its favorable matchup against most Magic Bounce Pokemon and common Defog users. It also has decent offensive presence, especially for a Stealth Rock setter, and a solid defensive typing, though Dialga's STAB attacks do have pretty mediocre coverage, leaving it with a dependence on coverage moves that it doesn't always have space for. Furthermore, if lacking Roar, it is setup bait for some Pokemon such as Calm Mind Arceus-Fairy. Lack of recovery hurts Dialga's viability, causing it to get worn down easily throughout a game. It's also fairly slow and lacks priority, leaving it vulnerable to fast attackers.