Thwacks are box-like enemies appearing in the game Mario & Luigi: Partners in Time. These enemies appear around in the area of Thwomp Volcano. They manifest as pink or green cubes that have a variety of facial expressions
In battle, Thwacks attack by twirling, then stomping their target to crush them and deal damage. The Thwacks' target is identified by their colour, with pink going toward Mario and green going toward Luigi. The Mario brothers have to counter them with their hammers. The second attack is charge that has the same tell. Thwacks can change their target mid-battle by changing their colour at the start of their turn, and also summon more of their kind.
When they run low on stamina, Thwacks can perform a third technique that involves splitting into two yellow blocks that charge and must be avoided by jumping.
Thwacks also appear in the Bowser boss fight in the shockwave attack. Here, Bowser creates a shockwave and Thwacks, dislodged by his tremors, rain down, shattering during their impact with the floor. The debris can be avoided by jumping.
There is a chance that Thwacks merge at the start of their fight. Thwack Totems are the result, and they can attack by dispatching their Thwacks to ground-pound (creating a shockwave that must be dodged by jumping), or spin to throw their Thwacks toward the Mario brothers, who must counterattack with hammers. You cannot damage them by ambushing them.
A Thwack Totem has all four Thwacks stacked up into a humanoid figure.
Wonder Thwacks are a stronger variety that lives at the shrine on Star Hill. They are red and blue rather than pink and green, respectively, and they glow. Wonder Thwacks have the same techniques that their normal counterparts do, but it is impossible to fight them as "Wonder Thwack Totems".
Wonder Thwacks also have a resistance versus a certain damage type, with their red form protecting them against fire damage, and their blue form protecting them against cold damage, but the opposite type is their weakness.