Age of Mythology: Retold

Centaurs are a useful unit that you can get in mission three of the Trident campaign. Simply worship Hermes as you age up and focus on wood and favour to continously produce centaurs. I needed about 10 worshippers and 7 woodsmen to have the influx of ressources to recruit them without pause.
They are good against anything but siege machinery. I got it about 20 minutes into the mission.

Just use the in-game editor to create a scenario. Use place objects to place some centaurs for player 1 and 100 villagers for player 2. Save the scenario and load it in skirmish mode. Run the scenario again if you don't get it first time round and its cumulative. You can do this for a lot of these achievement, just place the relevant units.