Stardust

Stardust is a consumable, Pokémon-related resource that can be used by Trainers to strengthen their Pokémon or perform trading. The amount of received Stardust in 30 minutes can be increased by 50% with the usage of a Star Piece.

Pokémon power up
The amount of Stardust required to power up a Pokémon is proportional to the percentage of the Pokémon's maximum potential CP. The cost of each power up can be from 200 to 15,000 Stardust. The cost of powering up a Lucky Pokémon is halved. Shadow Pokémon require 20% more Stardust while Purified Pokémon require 10% less Stardust to power up. The Lucky and Purified reduction can stack to become only 45% of original value.

There is no difference in the amount of Stardust required to power up a Pokémon regarding its evolution stage form. For instance, the same amount of Stardust is needed to power up Pikachu as Raichu that evolved from the same Pikachu.

Trading
Stardust is necessary to perform Pokémon trading. Pokédex unregistered, Shiny, and Legendary Pokémon require more Stardust to be traded. The amount required can be reduced by having higher friendship level with another Trainer.

Second Charged Attack unlock
Stardust can be also used to unlock the second Charged Attack of Pokémon with more than one Charged Attack. Unlock cost can be 10,000, 50,000, 75,000, or 100,000 Stardust. Shadow Pokémon require 20% more Stardust while Purified Pokémon require 20% less Stardust to unlock.

Purification
Stardust is necessary to purify Shadow Pokémon left by Team GO Rocket. Purification cost can be 1,000, 3,000, 5,000, or 20,000 Stardust.

Form Changing
Stardust can be used to change the forms of certain Pokémon. The cost can be either 2,000 or 10,000 Stardust.

Stardust bonuses from Pokémon
Chimecho and Audino always give extra Stardust when caught since their release. Starting from the Season of Celebration, more Pokémon give more Stardust than usual. This bonus does not apply to Shadow Pokémon.

Stardust events
This list does not include bonuses in Pokémon Spotlight Hour and Mystery Bonus Hour.

Trivia

 * Stardust multipliers from concurrent events may not stack with each other, only the highest one will apply. This does stack multiplicatively with Star Piece and Weather boost, however.