A collar designed to fit a dragon of any size, and will grow and shrink to fit. It has five gemstones, which can be activated and deactivated using a magic action, when touched.
Gem uses, left to right:

Onyx: control over creature, each hour, DC 18 Wisdom saving throw

Emerald: mania. The creature is aggressive to all creatures. No save. If a creature other than the one who activated the mania action attempts to alter any stone, the dragon will automatically use a bite or claw attack as a reaction. A creature can attempt an animal handling (wisdom) or charisma check (DC 15) to deactivate the stone. On a fail of five or more, the dragon will focus on that creature until attacked by another.

Ruby: Lock. The collar cannot be removed as long as the dragon is alive

Amethyst: breath suppression. The dragon cannot use breath weapons

Sapphire: sleep. The dragon sleeps until the stone is deactivated