The Thwomp Bros. are a pair of Thwomps that appear inside the Thwomp Volcano in Mario & Luigi: Partners in Time. They host two different games that the Mario Bros. must play in order to continue down the volcano.
The Bros. first run into the older of the Thwomp Bros. He explains that his younger brother (who resembles Mr. Thwomp) is up ahead and how the Thwomp Bros. Minigame Arcade is played. First, the older Mario Bros. must curl into a ball using the Bros. Ball technique. They then must roll into a gold cannon, which lights the fuse. Then Baby Mario must hit a switch, which sends Mario and Luigi into a pinball type area, where they must collect as many jewels as possible. After the plumbers have collected the jewels, the Thwomp gives the Baby Mario Bros. a certain number of chances (depending on how many jewels the older Mario Bros. collected) to stop a spinning roulette wheel on the wall in front of them for prizes. Baby Mario must hit a red switch three times and try and align three of the same symbols. The symbols are a Mushroom, Fire Flower, and Star. If Baby Mario aligns three Mushrooms or three Fire Flowers, the Bros. gets a certain number of coins or beans (depending on the difficulty setting). If he aligns three stars, the prize is one or more beans. The first play of this game is free; if the player chooses to continue playing, it costs 100 coins.
Deeper into the volcano, the four Mario Bros. find the younger of the Thwomp Bros. underneath a ! Block that must be hit in order to get rid of a large block restricting access deeper into the volcano. However, he will not let the Bros. hit the ! Block unless they play his game. To play, Mario and Luigi first Spin Jump into Baby Mario and Baby Luigi. The babies will propel into the air, and must get into a nearby Whirlwind. The babies then shoot into a pit, and must now collect jewels as they descend down the wide pit. To pass, the player must collect at least 30 of 50 jewels. After this has been accomplished, the Thwomp Bro. will take Baby Mario up to the ! Block that he needs to hit. The player can come back to play this game again whenever they like, but now the Thwomp Bro. challenges the player to collect all of the jewels, with the reward being a rare badge.