Frustration

Frustration is a Normal-type charged attack. All Shadow Pokémon have it upon capture. It is replaced with Return upon purification.

Frustration is retained by Shadow Pokémon if evolved. Charged TMs do not work on it normally. Shadow Pokémon cannot learn event exclusive moves if Frustration is still present during evolution.

Removing Frustration
During certain events, a Charged TM can be used to change a Shadow Pokémon's Frustration to other Charged Attacks that that Pokémon could learn normally. Shadow Pokémon and their evolution can learn exclusive attacks in future events as long as they forget Frustration.
 * Global take-over mini-event - March, 2020, 2 p.m. to 5 p.m. (local time)
 * Battle-themed event - July, 2020, 11 a.m. to 2 p.m. (local time)
 * Wooper Watch - December, 2020, 4 p.m. to December 2020, 4 p.m. (PST)
 * Special Raid Challenge - February, 2021, 11 a.m. to 2 p.m. (local time)
 * First part of Luminous Legends Y - May, 2021 10 a.m. to May , 2021 8 p.m. (local time)
 * A Looming Shadow Returns! - November, 2021 12 a.m. to November , 2021 8 p.m. (local time)
 * Team GO Rocket Strikes - January, 2022 12 a.m. to January , 2022 10 a.m. (local time)
 * All-Hands Rocket Retreat - April, 2022 12 a.m. to April , 2022 11:59 p.m. (local time)
 * Battle Weekend - July, 2022 12 a.m. to July , 2022 11:59 p.m. (local time)
 * Team GO Rocket takeover - November, 2022 12 a.m. to November , 2022 8 p.m. (local time)