Purified Pokémon are cheaper to power up in terms of Stardust and Candy. They also lose the Frustration move and have it replaced with Return. Return is not a very good charged move, but it can easily be replaced with a normal Charged TM. Remember, Frustration requires a special event to remove.
Purified Pokemon will have better Appraisal and receive 2 points towards all their IVs. This can potentially bring a 2-star Shadow Pokemon to a 3-star if it's purified. Purified Pokemon will receive a significant boost in Combat Power (CP).
Purifying a Shadow Pokémon will improve their appraisal and reduce the amount of Stardust and Candy required for them to Power Up, Evolve, or learn a new attack.
In PvE (Raids), you want to keep them unpurified, as they have higher DPS (damager per second) than their purified/regular counterparts, thanks to a 20% buff to their Attack, but on the flipside, because they see a 20% nerf to Defense, they go down faster, and that may hurt their TDO (total damage output), but the ...
Though a serious undertaking, Shadow Pokémon are incredibly useful allies in Raid Battles—their unique strength can help you defeat Raid Bosses quickly.
If you're attempting to complete research, attain a goal, or some other third oddity in the game, by all means, Purify all your Pokemon. But if you're seeking the most rare Pokemon in Pokemon GO, or you like Pokemon that WIN in Raids, keep your Shadows!
Purified Pokemon lose the 20% damage bonus made available to Shadows. Though this is less painful for certain Pokemon, others do benefit highly from remaining as a Shadow. The 2 IV increase is often dwarfed by the Shadow damage boost. There are exceptions, but the boost is largely preferred.
Purifying gives the Pokémon a significant increase in Combat Power and it will cost less candies to evolve. Make sure you Purify a Pokémon BEFORE you evolve it so you can use less candies.
While Return is OK on a normal-type Pokémon, it's not super great on anything else and can be replaced. Purified Pokémon also get IV boosts when powered up. Each stat goes up by two when purified, meaning if you catch a Shadow Pokémon with at least 13 Attack, Defense, and Stamina will turn into an 100% IV Pokémon.
Shadow Pokémon have a 20% boost to their Attack stats in both PvP and PvE (Raids and Gym battles) at the cost of a 20% decrease to their Defense stats. In PvE, this results in Shadow Pokémon being much stronger than their normal versions, since the huge increase in damage outweighs the lower bulk.
Purifying a Shadow Pokémon adds two to each of your IVs (to a maximum of 15) and improves your Pokémon's level to 25. So, adding this information to your Pokémon's current stats will give you its new CP.
Sadly, however, unlike evolving Pokémon, you don't get any XP for purifying Shadow Pokémon.
The user heals the target's status condition. If the move succeeds, it also restores the user's own HP. This move can't be used. It's recommended that this move is forgotten.
A lot of your shiny Pokemon won't be 3-stars. So if you want to hang on to a shiny, don't delete them. Some are rare, and your best stuff might be 2-stars.
Purifying a shadow Pokemon will add two points to each IV stat, so if you have a 13/13/13 shadow Pokemon, after purifying it, you'll be left with a 100% IV Pokemon.
Is it worth keeping 0 star Shadow Pokemon? Yes keep your shadow Pokemon unpurified. Shadow Pokemon works as angry Pokemon and will deal damage more faster then Normal or Purified Pokemon. The attack power of a Shadow Pokemon is boosted by 1.2x or 20%, making its fast attack hit significantly harder.
Pokémon Go Purified Pokémon benefits
The Stardust cost to powering up or teaching the Pokémon a secondary move will decrease by 10%. The Purified Pokémon will learn Return - a 3 bar Normal type move, which is great for Normal type Pokémon. IVs will be increased by 2 in every stat - Attack, Defence, HP.
NEVER purify, even if it would be 100%. Most Purified Pokemon have no advantages and even a 0% Shadow is much stronger in PvE.
Shadow Raids will also introduce Shiny Shadow Legendary Pokémon to Niantic's mobile game, and a new mechanic that will see players face tougher, “enraged” Shadow Pokémon.
At present, the only shiny Shadow Pokémon you can get are Grimer, Mawile, Squirtle, Charmander, and Bulbasaur. This information has been compiled through player accounts, official resources, and from the authoritative source on Niantic's hit mobile game, the Silph Road.
If anyone catches a shiny shadow Charizard in Pokémon Go, they are obligated to never purify it and name it “Red Eyes Black Dragon” or as close as possible to fit the character limits.
You cannot mega evolve shadow or clone Pokémon. You can mega evolve purified Pokémon, but they won't have a swirly white aura when mega evolved. You cannot use a mega evolved Pokémon to defend a gym.
Shadow Mewtwo is likely the best Pokémon in the entire game and has been for years, so be sure you purge it of Frustration to unlock its full potential. After you've dealt with the Legendaries, you should think about what you're doing with most of your time in the game.