Your students will LOVE this game. You need a dice and a board. The board can be from any board game. I used a candy land-esque board, and wrote "battle" on every 6-7 squares. Before students roll the dice, they must answer a math question. If they roll a one, they pick a chance card, and if they land on a "battle" square, they have to stop and do a multiplication-off with an opponent.
Questions cover a wide variety of 6-8th standards, including probability, percents, adding fractions, areas and perimeters, similar shapes, and transformations.
I used this to prepare for the end of year test!