Lucky Pokemon are a much underrated and under-utilized feature in Pokemon Go. They provide the best way to get the strongest Pokemon on the game.
As a result you should go out your way to get as many as possible. Here's how to go about finding them in Pokemon Go.
Lucky Pokemon behave and look like normal Pokemon but have one vital difference - they cost half the Stardust to power them up in comparison.
Stardust in any large quantity is hard to come by, so if you're a competitive player who wants to get Pokemon to the maximum level of 40, obtaining Lucky Pokemon is essential.
Trading specific Pokemon is currently the best way to get lucky Pokemon.
Since September 2018, Niantic have changed how easy it is to get lucky Pokemon. If two trainers are trading Pokemon which were caught in July or August 2016, and one of the trainers has had less than 10 that are lucky, then both Pokemon in the trade will be lucky.
How easy this is to achieve will vary from trainer to trainer. Some will have played Pokemon Go since its release (July 2016) and will have a stockpile of older Pokemon. Others may be newer to the game in which case they'll need to find someone with older Pokemon.
All trades have a chance of resulting in both Pokemon being lucky. However, trading older Pokemon has a greater chance of making them lucky.
The exact percentages of obtaining a lucky Pokemon based on the age of it are unknown. It has been speculated that when two are traded, the game will take the average age of the two and put a percentage on it based on that.
Others have speculated that there is a limit to how many you can obtain over a certain time period.
To be safe and not waste rare Pokemon from 2016, it's probably wise to make sure one trainer has had less than 10. If you are willing to run the risk, then make sure you don't do several trades without them being lucky.
In April 2019, Niantic introduced the Pokemon Go lucky friends feature. It is detailed in the link above but essentially if you are best friends with another trainer, each time you interact, you have a chance of becoming lucky friends.
Becoming lucky friends guarantees your next trade to result in lucky Pokemon for the both of you.
Lucky Pokemon are guaranteed to have IVs of 12 across the board (80%). Like shiny Pokemon, they can also spawn in the wild, although this is rare.