Elder BrainLarge aberration
Creature Sense. The elder brain is aware of the presence of creatures within 10 kilometers of it that have an Intelligence of −3 or higher. It knows the distance and direction to each creature, as well as each one’s Intelligence, but can’t sense anything else about it. A creature protected by a psychic fortress spell augmented to mind blank, a nondetection spell, or similar magic can’t be perceived in this manner.
Legendary Resistance (3/day). If the elder brain fails a saving throw, it can choose to succeed instead.
Magic Resistance. The elder brain has advantage on saving throws against spells and other magical effects.
Spellcasting. The elder brain’s spellcasting ability is Intelligence (spell save DC 20, +12 to hit with spell attacks). It has 27 mana, a mana limit of 5, regains all expended mana when it finishes a long rest and regains half its total mana (rounded up) when it finishes a short rest. It knows the following spells:
1 mana: agonizing rebuke, call to mind, confusion, ego whip, haze senses, meld mindcrystal, mind over body, mind spike, mind trap, psychic fortress, sending, sense minds, thought shield, wandering mind
5 mana: mind seed
1/day: plane shift (self only)
Telepathic Hub. The elder brain can use its telepathy to initiate and maintain telepathic conversations with up to ten creatures at a time. The elder brain can let those creatures telepathically hear each other while connected in this way.
Tentacle. Melee Weapon Attack: +7 to hit, reach 9 m. Hit: 20 (4d8 + 2) bludgeoning damage. If the target is a Huge or smaller creature, it is grappled (escape DC 15) and takes 9 (1d8 + 5) psychic damage at the start of each of its turns until the grapple ends. The elder brain can have up to four targets grappled at a time.
Mind Blast (Recharge 5–6). The elder brain magically emits psychic energy. Creatures of the elder brain’s choice within 10 meters of it must succeed on a DC 20 Will saving throw or take 32 (5d10 + 5) psychic damage and be stunned for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Psychic Link (1/turn). The elder brain targets one incapacitated creature it can perceive with its Creature Sense trait and establishes a psychic link with that creature. Until the psychic link ends, the elder brain can perceive everything the target senses. The target becomes aware that something is linked to its mind once it is no longer incapacitated, and the elder brain can terminate the link at any time (no action required). The target can use an action on its turn to attempt to break the psychic link, doing so with a successful DC 20 Will saving throw. On a successful save, it takes 10 (3d6) psychic damage. The psychic link also ends if the target and the elder brain are more than 10 kilometers apart, with no consequences to the target. The elder brain can form psychic links with up to ten creatures at a time.
Sense Thoughts (1/turn). The elder brain targets a creature with which it has a psychic link. The elder brain gains insight into the target’s reasoning, its emotional state, and thoughts that loom large in its mind (including things the target worries about, loves, or hates). The elder brain can also make a Deception check with advantage to deceive the target’s mind into thinking it believes one idea or feels a particular emotion. The target contests this attempt with a Insight check. If the elder brain succeeds, the mind believes the deception for 1 hour or until evidence of the lie is presented to the target.
Legendary Actions (3)
Only one legendary option can be used at a time and only at the end of another creature’s turn. The elder brain regains spent legendary actions at the start of its turn.
Break Concentration. The elder brain targets a creature within 20 meters of it with which it has a psychic link. The elder brain breaks the creature’s concentration on a spell it has cast. The creature also takes 2d4 psychic damage per mana of the spell.
Psychic Pulse. The elder brain targets a creature within 20 meters of it with which it has a psychic link. Enemies of the elder brain within 2 meters of that creature take 10 (3d6) psychic damage.
Sever Psychic Link. The elder brain targets a creature within 20 meters of it with which it has a psychic link. The elder brain ends the link, causing the creature to have disadvantage on all ability checks, attack rolls, and saving throws until the end of the creature’s next turn.
Tentacle. The elder brain makes a tentacle attack.
No concoctions, maneuvers, or spells
All monsters in this system should have maneuvers or spells. You should add some maneuvers or spells to this monster. If you do so, please make a suggestion on github so I can finish adding maneuvers and spells to all monsters via https://github.com/mlenser/kryx-rpg-issues/issues/9