Adult Green Dragon

The monster can breathe air and water.

If the monster fails a saving throw, it can choose to succeed instead.

The monster makes three Rend attacks. It can replace one attack with a use of Spellcasting to cast Mind Spike (level 3 version).

Melee Attack: +11 to hit. reach 5 ft. Hit: 2d8 + 6 slashing plus 2d6 poison damage.

Constitution Save: DC 18. target: 60-foot cone, enemy. Failure: 16d6 poison damage; success: half.

The monster casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability: At Will: Detect Magic, Mind Spike (level 3 version) 1/Day: Geas

For the duration, you sense the presence of magical effects within 30 feet of yourself. If you sense such effects, you can take the Magic action to see a faint aura around any visible creature or object in the area that bears the magic, and if an effect was created by a spell, you learn the spell's school of magic. The spell is blocked by 1 foot of stone, dirt, or wood; 1 inch of metal; or a thin sheet of lead.

You drive a spike of psionic energy into the mind of one creature you can see within range. The target makes a Wisdom saving throw, taking 3d8 Psychic damage on a failed save or half as much damage on a successful one. On a failed save, you also always know the target's location until the spell ends, but only while the two of you are on the same plane of existence. While you have this knowledge, the target can't become hidden from you, and if it has the Invisible condition, it gains no benefit from that condition against you. Using a Higher-Level Spell Slot. The damage increases by 1d8 for each spell slot level above 2.

You give a verbal command to a creature that you can see within range, ordering it to carry out some service or refrain from an action or a course of activity as you decide. The target must succeed on a Wisdom saving throw or have the Charmed condition for the duration. The target automatically succeeds if it can't understand your command. While Charmed, the creature takes damage if it acts in a manner directly counter to your command. It takes this damage no more than once each day. You can issue any command you choose, short of an activity that would result in certain death. Should you issue a suicidal command, the spell ends. A Remove Curse, Greater Restoration, or Wish spell ends this spell. Using a Higher-Level Spell Slot. If you use a level 7 or 8 spell slot, the duration is 365 days. If you use a level 9 spell slot, the spell lasts until it is ended by one of the spells mentioned above.

The dragon uses Spellcasting to cast Mind Spike (level 3 version).

You drive a spike of psionic energy into the mind of one creature you can see within range. The target makes a Wisdom saving throw, taking 3d8 Psychic damage on a failed save or half as much damage on a successful one. On a failed save, you also always know the target's location until the spell ends, but only while the two of you are on the same plane of existence. While you have this knowledge, the target can't become hidden from you, and if it has the Invisible condition, it gains no benefit from that condition against you. Using a Higher-Level Spell Slot. The damage increases by 1d8 for each spell slot level above 2.

Constitution Save: DC 18. target: 20-foot sphere, creature. Failure: 2d6 poison damage.

The monster moves up to half its Speed, and it makes one Rend attack.