This new Strange Red Egg requires a Trainer to walk 12km to hatch. It contains some old Dark and Poison-type Pokemon and some new Pokemon that will have their first debut through the Strange Eggs.
Interestingly, this is the second time Niantic adds a new distance of eggs since the beginning of the game back in 2016. They started with 2km, 5km, and 10km Eggs, then they added the Gift 7km Eggs, and now we have the Strange Eggs.
Unlike the rest of the eggs, the Strange Red Eggs can be obtained through battles with the Team Rocket Leaders and Team GO Rocket Grunts. Bare in mind that you need to have a free egg slot if you want to get it. We get it, this is difficult to maintain, but we hope that some things will be fixed in the future.
Niantic has kept the interest in the game by constantly shuffling the Pokemon available in eggs, but it seems like nowadays they are adding more basic ones, rather than rarer ones. We just hope that this will be fixed as soon as possible.
Here is the list of Pokemon that can be hatched from Strange Eggs 12km Eggs.
12KM Egg Hatching Chart
NOTE: Highlighted Pokemon can be shiny.
For last, here is the list of Pokemon hatching from 2km, 5km, 7km, and 10km Eggs.