With the latest update, Niantic added a brand new kind of quality for Pokémon.
Will they appear in the wild as shiny Pokémon do?
Can all Pokémon right now be lucky?
Are there any differences apart from the background effect?
Will there be a noticeable difference when on the map?
Will a lucky Pokémon be for everyone or randomly for each user (like shiny)?
Best Answer
To answer your questions, based on the patch notes and the official blog:
No, only pokemon that are traded can get the lucky trait.
As it looks right now, any pokémon that can be traded can get the lucky trait.
Lucky pokémon require 50 % less stardust to power up than pokémon without the lucky trait.
Not applicable since lucky pokémon don't appear in the wild.
Lucky pokémon are a random chance when trading, with a higher chance for pokémon which have been in storage for a while. When a trade triggers the Lucky trait, both pokémon receive the trait.
Source: https://www.polygon.com/pokemon-go/2018/7/23/17602604/pokemon-go-update-lucky-pokemon and the links within.