A game to help students practice by, in, under, and on. First is a short review of the vocab. Then, each slide reveals balls in several positions and students gamble on where the balls will be.
I drew a grid on the blackboard to make it easier to visualize the points and where the students were betting. I started with five points and doubled them for each correct gamble, making sure to warn the students not to go all in. One eventually did, but the class agreed to loan him 5 points so he could keep playing.
I did this with a ~very~ small class so each student chose for themselves where to bet, though with a larger class maybe it would be better to split everyone into groups. I would also recommend increasing the stakes as there are less and less balls, as some students got left behind and couldn't really catch up. Make sure to review the forms of each sentence (i.e. The ball is under the table) and enforce vocab usage. I also made the students tally their own points to review the lesson.
P.S. The presentation sometimes lets you see where the balls are when flipping to the next slide, so I had the students close their eyes.