Cosmog @ Assault Vest
Ability: Unaware
Level: 5
Tera Type: Any
EVs: 12 HP / 204 Atk / 28 Def / 28 SpD / 220 Spe
Adamant / Jolly Nature
- Teleport
- Splash
Do not use Cosmog. Though using a Legendary in LC may appeal to you, Cosmog will almost always faint before it can even damage opponents, no less knock one out. This has it serving more as a handicap than an actual, practical Pokémon. Regardless, let me contradict what I just said and provide a set that allows it to do something!
Assault Vest, though granting a 1.5x multiplier to Sp. Def, restricts the usage of Status moves. As Cosmog can only learn two Status moves total, this ensures Cosmog can hold this item to attack with Struggle! The EV spread maximizes Attack and Speed, where an Adamant or Jolly nature can be chosen to add an additional stat point to the former or latter. 12 HP EVs ensure Cosmog has an odd HP stat, allowing it to use Struggle five times if left unharmed by its opponent. The remaining EVs are put into its Defensive stats, though it's not likely to live a hit. You're likely not going to Terastalize Cosmog, but if so, it's best to choose one that has multiple resistances and/or immunities, such as Steel or Ghost, one that avoids harmful status conditions, such as Fire or Electric, or one that resists Knock Off, one of Cosmog's greatest weaknesses, such as Fairy or Fighting.
