In Ogre Under, each player controls a merchant and a donkey who are transporting goods across an ogre-infested bridge, headed for the market in the city. In each round, players select an action card from their hand and then simultaneously reveal them. Action cards allow players to perform one of the following actions:
- Flip over one of the eight bridge cards, potentially revealing an ogre that scares any merchants and donkeys on that card backwards a number of spaces.
- Protect their merchant from a possible ogre attack.
- Move their donkey forward, up to their merchant's current location.
- Bet on whether the next market price card to be revealed will be higher or lower than the current one. Correct bets move your merchant forward a number of spaces (based on how risky the bet was), while incorrect bets move your merchant back to your donkey's current location.

Play continues round after round until one or more players win by having both their merchant and their donkey in the city market at the end of a round.