Hotheads (パサラン, Pasaran) are items that, when thrown, will slide across the ground releasing bursts of sparks and damaging opponents of the thrower. They can be made to grow bigger by attacking them, with bigger Hotheads dealing more damage and knockback. However, in contrast to what its Brawl trophy says, there is an upper limit to how large the Hothead can become (roughly three times its original diameter).
In Super Mario World, Hotheads were enemies that appeared inside Wendy Koopa's Castle in World 6, Chocolate Island. This level largely consisting of stone blocks, which had Hotheads constantly moving around them. Unlike those in Smash, they were not enlarged by fire and they never disappeared, though small and large versions of the enemy appeared together.
In a Hothead's initial state, it is an item that can be picked up and thrown. It will be set in motion once thrown, and once the Hothead lands on the ground or a platform, it will move along the surface in the direction it was thrown and periodically release sparks, which are almost twice as strong as a smash-thrown Hothead of the same size.
Hotheads can be attacked, and if a Hothead is attacked by flame or electric attacks (or any attack in Ultimate), it will grow larger; in can be attacked both before and after setting it in motion. A Hothead will reach maximum size after it takes approximately 30% damage. However, if it is undamaged and takes more than 30% damage at once, it can gain OHKO power; as an extreme example, knocking five Soccer Balls into a Hothead using Marth's Critical Hit would cause the Hothead to deal 140% damage or more and become impossible to reflect.
If it is thrown onto solid terrain, the Hothead will cling onto the surface, travelling along the walls or ceilings. However, if it is on soft terrain, the Hothead will fall off of the edge, and continue to fall until it lands again (or falls off the screen). In Ultimate, Hotheads appear to change their direction when they travel offstage on flat surfaces instead of disappearing.
Hotheads eventually disappear in an amount of time inversely proportionate to their size (that is, bigger ones vanish faster). A travelling or thrown Hothead can be reflected, which will change its ownership and reverse its direction of travel.
Note: All of these damage percentages were taken with an uncharged Hothead.
An item that, when tossed, sticks to the terrain and moves, causing damage to those it touches. Whoever threw it won't take damage. It will grow larger if it's attacked, which ups its attack range. However, an increase in size corresponds to a decrease in the time it stays on the screen. A really big Hothead will take up the entire screen, and is quite a sight to behold.
Hothead is featured as a Spirit.
In addition to the above, equipping the Plasma Wisp or Zip Support Spirits will give the player a Hothead at a start of a match.