If I use Unown VSTAR's "Star Cipher" attack while Dunsparce with "Mysterious Nest" Ability is in play, are my opponent's colorless Pokemon's Weakness set to {P} or do they have no Weakness at all?
The Star Cipher attack would switch your opponent's Pokemon's weakness to {P}, but then Dunsparce's Mysterious Nest would change all colorless Pokemon to no weakness.
Source: TPCi Rules Team (2022-11-10)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH8_207
SWSH8_207
SWSH12_66
SWSH12_66