Talisman: Digital Edition

Heavily RNG based. Start a game with the Sacred Pool expansion activated and play as the Dread Knight. Run around until you encounter the Fel Steed and defeat it in battle. It has a Strength of 7, and though it's unlikely, you can manage to defeat it with only your starting Strength as long as you get a 6 and it gets a 1. Keeping your Warhorse and any other increase to Strength will ofcourse help, but if you encounter it without any such things you can also choose to exit the game and reenter to retry the battle as many times as necessary. Defeat it and you'll unlock the achievement.