Yellow dragons are to gold dragons as fool's gold is to real gold. They physically appear very similar to gold dragons, and an older yellow dragon's scales even have a slight sheen, but in reality, the vicious and brutal yellow dragons are entirely unlike the majestic gold dragons.
However, the mimicry of a yellow dragon is flawed in several key ways. No yellow dragon can breathe fire or the weakening gas of a gold dragon: their breath is charged with the fury of lightning, so a yellow dragon avoids using its breath weapon if it risks exposing itself, often hunting during storms when its breath could be dismissed as a bolt of lightning, while some study magic to replicate the effect of a searing storm of fire. Yellow dragons are also noticeably smaller and weaker than gold dragons, though yellow dragons claim that they were always the smallest of the clutch if this threatens to reveal their deception. Most revealing of all is that, even though a yellow dragon's scales have a slight sheen, it is never to the same degree as a gold dragon.

Conniving and Cunning. Yellow dragons are deceitful by nature, avoiding the truth whenever they can, finding amusement in misleading other creatures. A yellow dragon hates creatures more powerful than itself, and seeks to attack and devour them in secrecy.
A yellow dragon loves the taste of humanoid flesh, though it rarely indulges its hunger for fear of outing itself. Interlopers that grow curious and begin investigating the lair of a yellow dragon are seen as fair game by yellow dragons, devouring them to indulge its hunger and to keep its secret.
A yellow dragon that has its secret revealed ruthlessly destroys any creatures that revealed it, indiscriminately attacking and levelling nearby settlements and taking anything that it wants.

Similar Treasures. Attempting to appear as similar as possible to gold dragons, yellow dragons stock their hoards with treasures valued by gold dragons, such as pearls, and places magical wards within its vaults, though above all else, a yellow dragon craves yellow gemstones, as it sees yellow as the most beautiful and majestic of all colors by far.

A Yellow Dragon's Lair

A yellow dragon prefers to build its lair in places that a gold dragon might be found, to aid in its mimicry.

Lair Actions

On initiative count 20 (losing initiative ties), the dragon takes a lair action to cause one of the following effects; the dragon can't use the same effect two rounds in a row:

• The dragon creates a cloud of fog as though it had cast the fog cloud spell. The fog lasts until initiative count 20 on the next round.
• A bolt of lightning strikes a point the dragon can see within 120 feet of it. Each creature within a 20-foot radius centered on that point must make a DC 15 Dexterity saving throw or take 10 (3d6) lightning damage.
• The dragon creates an illusory replica of itself. The replica acts on the same initiative as the dragon, but cannot damage or otherwise harm creatures or objects. Physical interaction with the image reveals it to be an illusion, because things can pass through it. The image fades on initiative count 20 on the next round.

Regional Effects

The region containing a legendary yellow dragon's lair is warped by the dragon's magic, which creates one or more of the following effects:

• Thunderstorms rage within 6 miles of the lair.
• Gems and pearls within 1 mile of the dragon's lair that aren't a part of its hoard seem duller than usual.
• There's a noticeable increase in the populations of creatures that hunt by mimicry.

If the dragon dies, these effects fade over the course of 1d10 days.