Danger Zone

The burning red Danger Zones are as dangerous as their name implies. Touch them with more than 100% damage, and you'll be instantly KO'd. Danger Zones are stage hazards that appear in both versions of Super Smash Bros. 4 and Super Smash Bros. Ultimate. Characters who touch them will either take damage or be instantly KO'd without ever passing the blast lines.

In
Danger Zones make their debut in in Smash Run. Some "Defeat Them All!" challenge rooms feature floors which become Danger Zones every few seconds, instantly KOing the player regardless of accumulated damage. Dotted throughout the main map are Danger Zones in the form of lava-colored spiked balls, which also KO regardless of damage.

In the "Run!" and "Climb!" final battles, Danger Zones are placed throughout the course. They appear as either pools of lava or as bunches of spiked balls. Their effect is the same as in the Smash Run itself: if a fighter hits one, they are instantly KO'd regardless of their current damage and are revived further back/down in the stage. Unlike in the Smash Run, however, Danger Zones disappear after being hit once, allowing all players to more easily traverse the stage.

In
Danger Zones make their next appearance in Super Smash Bros. for Wii U. In The Great Cave Offensive Danger Zones are placed throughout the stage, and take the form of lava. If a fighter makes contact with one, they will take 25% flame damage and heavy knockback, but if they had equal to or over 100% damage before touching it, they will be instantly KO'd. If the KO belongs to another fighter when this event occurs, that fighter gains credit for the KO. It is possible for a character to tech on a Danger Zone without taking damage or getting KO'd, but this is rather difficult.

Danger Zones are also found inside during the Master Core battle at the end of, more prominently during the second wave than the first. Unlike the examples above, these Danger Zones take the form of either subtle yellow outlines on the walls, more expansive pools of acid resembling those found on Brinstar, or, in one instance, a yellow spiky protrusion from a platform. These danger zones will also One-hit KO the enemies inside the fortress. Like in The Great Cave Offensive, touching one while under 100% damage will inflict 25% damage and high knockback, but touching one while at or over 100% damage will instantly KO the player, unless teched against.

In Super Smash Bros. Ultimate
The Great Cave Offensive returns in Ultimate and has the same Danger Zones as in for Wii U. Aside from no longer dealing flame elemental damage, they are functionally the same. They can no longer be teched against under any circumstances.

Trivia

 * Danger Zones may trace their design to the lava pools in the original version of The Great Cave Offensive from Kirby Super Star and Kirby Super Star Ultra.
 * In for Wii U's Stage Builder, areas of lava strongly resembling Danger Zones can be added, but they are not named Danger Zones and do not behave the same way, only inflicting 10% damage upon contact and lacking the instant KO effect.
 * In both versions of Smash 4, the instant-KO effect resembles the effect seen during a regular blast KO, but as if viewed head-on. Despite this, there is no way to view an actual blast KO head-on like this under any circumstances.
 * The Prima Games Guide for Super Smash Bros. for Wii U mentions that Danger Zones will instantly KO their target if that target has their damage metre knocked to 125% or higher as a result of contact. Barring hacks that alter the Danger Zones's damage, this would be true if the damage were counted after the Danger Zone's damage is applied.