Thwacks are box enemies with faces that live on Thwomp Volcano during the events of Mario & Luigi: Partners in Time. In fact, Thwacks are very similar to Thwomps in appearance and mannerisms. As such, Thwacks may be a derived species of Thwomp or a separate, but closely related, species. Thwacks come in two colors: red and green. Red Thwacks have blue eyes while green Thwacks have yellow eyes. Thwacks also make a variety of facial expressions.
In battle, Thwacks employ a variety of attacks. Before each attack, a Thwack twirls and either remains the same color or changes into a different color. If green, the Thwack attacks Luigi; if pink, the enemy attacks Mario. After twirling, the Thwack may attempt to crush the Bro. of its choice. As the Thwack hovers over the hero, the baby Bro. should counter with a Hammer strike. Additionally, Thwacks may fly low, attempting to ram into a Mario brother. In this case, Mario or Luigi should jump to dodge or counter the attack. Thwacks can also summon more Thwacks to join the battle.
Occasionally, the Thwack may turn yellow (instead of red or green). When this happens, the Thwack will attempt a sacrificial attack in a last ditch effort to destroy the Mario Bros. After turning yellow, the Thwack splits into two boulders, and each rock rolls into a brother. This attack can be avoided by jumping.
In the battle against Bowser and Baby Bowser, the former uses a shock wave attack that can, depending on the speed of the shock wave, can send all kinds of Thwacks raining down on the quartet. The debris can be jumped over.
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