Mrs. Thwomp is a female Thwomp in Mario & Luigi: Partners in Time and one of the bosses of the game. She is married to Mr. Thwomp and is very easily angered. She lives in Thwomp Volcano, and, unlike all other Thwomps, she is shaped as a boulder and has arms. She is also the first explicitly female Thwomp. Her battle style is similar to Trunkle, a boss from Mario & Luigi: Superstar Saga.
In the game, when Mario, Luigi, Baby Mario and Baby Luigi come to the volcano, the volcano erupts. With E. Gadd's help, they are able to put the fire out using the Hydrogush 4000. Mr. and Mrs. Thwomp, however, wait each year for the volcano to erupt immediately, so when Mario and Luigi stop the eruption, they are upset. As the brothers make their way to the summit, Mrs. Thwomp scolds them and decides to battle them. During the battle, she has a few attacks. The first one involves slamming the ground and producing a shockwave for the brothers to jump over. The second attack involves her shooting rocks at them alternately. If she shoots a rock from her right, it hits Mario, if from the left, it hits Luigi. She will also occasionally fire a rock between the brothers as a fake out to keep them off guard for the other rocks. If the brothers successfully hit a rock with their Hammer, they will get a healing item or a Bros. Item. After losing at least 150 HP (230 in Japan and British English regions), she splits into four small versions of herself. After taking even more damage in this phase, it is revealed that some Goombettes help her as decoys when she shrinks. They have slightly imperfect disguises, however, which the player can use as a clue to which to attack; one has a chip on its head, another has fewer teeth than the real Mrs. Thwomp, and the other has sharp teeth instead of blunt ones. In this form, Mrs. Thwomp attacks by hopping in front of Mario or Luigi, at which point either should use their hammer to repel the attack and damage her.
After being defeated, Mrs. Thwomp gets sad and her husband attempts to calm her down by scolding the Mario Bros. for "hitting a lady." After the brothers reveal that they're trying to save Princess Peach, a lady, Mr. Thwomp is pleased and offers to take the brothers into Thwomp Caverns. Mrs. Thwomp then asks to come along, but Mr. Thwomp, knowing her weight would be too much for him to safely carry, disdainfully says no. She becomes furious in response and knocks Mr. Thwomp into the volcano with a hard body slam, before muttering that Mr. Thwomp is a "jerk." From that point on, if spoken to again, Mrs. Thwomp repeats this line ("JERK" in big letters).
Names in other languages