Age of Empires II: Definitive Edition

When you're on the main menu, click on the blue shield (Standard Game) and then just copy paste these settings:



Next, start the game and the first thing you want to do is zoom all the way out, as far as possible. Now look for animals, there will be lots of them and all different kinds, but the ones we're looking for are either goats or sheep. If you see goats, what you want to do is quit your match and go all the way back to the main menu (so don't just press 'restart', that will give you goats again). Once you're in the menu, click on the blue shield again, all the settings should be the same so don't worry about that. Just keep starting matches until you see sheep in your game. This is actually random for everyone, I think there's a 50/50 chance so it shouldn't take too long.

If you're certain that there are sheep in your game, the next thing you need to do is press the 'idle villager' button on top (orange/yellowish) and simply click right next to a sheep, not on the sheep since that'll make you hunt and kill it. What you want to do is 'own' the sheep (if it has the same coloured collar as your player colour, then you know it's yours).

Now do this 20 times in total. Press the orange/yellowish button on top, look for a nearby sheep, make your villager go stand near it so it becomes yours. Press the orange/yellowish button on top, look for a nearby sheep, make your villager go stand near it so it becomes yours. Etc, etc.

Just for clarification; you don't need to group them together or anything like that. I've seen guides/comments of people making this achievement way harder than it actually is. Just make sure there are sheep in your game, and then go stand next to them so they'll become yours, do this 20 times and that should make it pop.

I modified LMEPHISTO's solution for the quick win method for all civs with the below modification to get this achievement.
Civilization: Any
AI Opponents: 5 or 6
Game Mode: Wonder Race
Map Style: Standard
Map Size: Small
AI Difficulty: Easiest
Resources: Infinite
Population: 200
Game Speed: Normal
Reveal Map: All Visible
Starting Age: Post-Imperial Age

Screenshot of settings -

You may have to close game and restart until you see the 4 sheep near your town center

Once you have sheep and not other livestock, make one villager build 4-5 houses, set the two other villagers to build the wonder and then build additional villagers to continue the monument but the idea is not to win. Send scout and other villagers if needed out to snag the other sheep at all other civ locations. The other civs will only concentrate on building the wonder and will ignore the sheep. Once you have 20+ tagged for your civ send them back to the town center and once they are close the achievement will pop.

Just play a huge map in nomad mode. Use Mongols to have more LOS and start at feudal. The achievement will trigger when you find the 20th sheep.

Easiest way I found to get this achievement is with the following settings.

Random map mode, Black Forest with 7 AI players, Celts civilisation, Easiest AI, Tiny map size and standard starting resources (sheep didn’t want to spawn with higher rss levels...?)

As all players start with up to 8 sheep near their TC, the small map size and number of players makes a lot of sheep spawn very close to your TC.

Just send your scout to pick up all the sheep you can from the enemy AI TC, as the Celts can effectively convert sheep. Send them back to your TC and get 20 and you’re done. Took me under 2 minutes to get the achievement.

Hope this helps