Animate Corpse Dragon

You profane the corpse of an Adult or older dragon to raise the ultimate undead monstrosity. You can cast this spell only at night. Once you complete the ritual, the dragon arises as an empty, rotting shadow of its former self. Treat its statistics as those of an Adult White Dragon, with the exception of the following:

• It loses immunity to cold damage, gains resistance to cold and necrotic damage, and gains a vulnerability to radiant damage.
• If the corpse is skeletal, it gains resistance to piercing damage and vulnerability to bludgeoning damage.
• It is immune to the following conditions: charmed, exhaustion, frightened, paralyzed, poisoned.
• Its breath and bite deal necrotic damage instead of cold damage.
• It cannot take legendary actions.

As a bonus action on each of your turns, you can mentally command the dragon if it is within 120 feet of you. You decide what action the creature will take and where it will move during its next turn, or you can issue a general command such as to guard a particular chamber or corridor. If you issue no commands, the creature only defends itself against hostile creatures. Once given an order, the creature continues to follow it until its task is complete.

The creature is under your control for 24 hours, after which it stops obeying any command you have given it. To maintain control of the creature for another 24 hours, you must cast this spell on the creature before the current 24-hour period ends. If you are casting this spell to maintain control of an existing corpse dragon, you may do so as a ritual and it requires no material components.