Question: how to unlock all characters in mario party?
Answer: Pom Pom: Shows up in the Party Plaza after completing the Salty Sea section (world 5) of Challenge Road. ... 
Diddy Kong: Similar to Pom Pom, you have to complete the Chestnut Forest section (world 2) of Challenge Road to unlock Diddy Kong.
Donkey Kong: To unlock Donkey Kong, play River Survival three times.