The Battle of the Elder Brain

What this combat is about

Elder Brain (CR 25) fight plan using the high-level principles we discussed

Setup assumptions

• High-level party loaded with magic items (roughly APL 18–22 territory so the CR 25 feels appropriately threatening but not auto-TPK).
• Classic Elder Brain lair: large cavern with a deep brine pool in the center (Elder Brain floats in/over it). Surrounding stone walkways, pillars, and a couple of higher ledges. The main entrance is a doorway/tunnel sized for Medium/Large creatures only — too narrow for your two Huge iron golems.
• Supporting cast for action economy (do not run it solo):
  • 2–3 brain golems already budded (CR ~10 each, Large constructs with slam + mind blast).
  • 2–4 mind flayer thralls or dominated high-level thralls (warriors/casters) for extra actions and focus-fire.
  • Optional: a few lower thralls as disposable mooks.

Secondary objectives / engagement levers

• Disrupt or damage the brine pool (acid/sonic attacks or specific actions reduce the Elder Brain’s regeneration or force it to spend actions).
• Destroy a central “telepathic hub” crystal or node that boosts its awareness/range (makes domination harder once gone).
• The golems themselves become a timed reinforcement that changes the action economy.

Getting the two Huge iron golems into the room within a few rounds Iron golems (especially Huge) have massive Strength. Best options that keep the fight dynamic:

1. Smash entry (cleanest): The walls/doorframe around the entrance have reduced hardness or are already cracked/weakened by the colony. Each golem can take a full-round action (or two rounds of effort) to smash a Large-to-Huge opening. On round 3–4 they burst in with a dramatic wall-collapse, creating difficult terrain/rubble and giving the party sudden heavy melee support.
2. Timed collapse: The Elder Brain’s own psychic pressure or a lair effect starts cracking the ceiling/wall on round 2. The golems finish the job on round 3–4.
3. Party assist: A disintegrate, passwall, stone shape, or even a high-Strength character + adamantine weapon can widen the opening in 1–2 rounds so the golems can squeeze/force through.
4. Avoid pure teleport solutions unless the party already has reliable ways to move Huge constructs — the goal is to make their entry a visible, impactful event rather than off-screen magic.

Extract does nothing to the golems (constructs are immune). They are excellent against the Elder Brain’s tendrils and can tank mind blasts better than the PCs.

Round-by-round tactics (up to 10 rounds)

Pre-combat / Round 0 Elder Brain already knows the party is coming via telepathic awareness (350 ft). It has pre-buffed (shield, displacement, resist energy, etc.) and positioned its brain golems and thralls. The brine pool is glowing; platforms are clear.

Round 1 – Opening salvo (action economy + control)

• Mind Blast (60-ft cone, DC 31 Will or stunned 3d4 rounds) aimed at the densest group of PCs as they enter.
• Quicken mass suggestion (“Drop your weapons and kneel” or “Flee the chamber”) or charm monster on a key caster.
• Brain golems and thralls advance or take cover and ready actions.
• Elder Brain stays in the pool (hard to reach).

Round 2 – Divide and dominate

• Dominate Monster (DC 27) on the biggest physical threat or the party’s main controller.
• If anyone closed to melee range, full attack with 4 tendrils + improved grab (set up extract next round).
• Greater dispel magic or chain lightning on clustered/buffed PCs.
• Minions focus any stunned targets.

Round 3 – Golem entry + escalation

• The two Huge iron golems smash through the wall/entrance (or the ceiling partially collapses). They enter with a roar of falling stone — new difficult terrain and a sudden shift in action economy.
• Elder Brain reacts with maze or prismatic sphere if the golems look threatening, or energy drain / telekinesis to hurl someone into the brine.
• Buds a fresh brain golem if one has fallen (once per day limit still applies overall).

Round 4 – Mid-fight pressure

• Mind Blast recharges and fires again if available.
• Focus tendrils on any grappled or dominated targets for extract (instant kill on success).
• Uses screen or displacement to stay hard to target while minions and remaining brain golems swarm.
• Secondary: if the party is damaging the pool or hub crystal, the Elder Brain spends an action to defend it or telekinetically shove attackers away.

Round 5 – Phase shift

• At roughly half HP or when the golems are fully engaged, the Elder Brain changes tactics: prismatic sphere around itself (or a wall of force equivalent via spells), then insanity or dominate on whoever is still free.
• Remaining thralls throw themselves at the golems to buy time.
• Environment: parts of the walkways start cracking or psychic energy fields force Will saves (or just difficult terrain).

Round 6–7 – Attrition and extraction

• Continues cycling Mind Blast when available, tendril grabs on isolated PCs, and high-level spells (Mordenkainen’s disjunction if the party is loaded with items, chain lightning, energy drain).
• Brain golems mind-blast and slam.
• If a PC is extracted, the Elder Brain gains a temporary boost or simply uses the moment for dramatic effect and more domination.
• Golems should be smashing brain golems or trying to reach the pool by now — let them feel useful.

Round 8–9 – Desperation / high drama

• If still above ~25% HP: plane shift attempt on itself or a dominated PC, or astral projection contingency.
• Full tendril attacks + extract on anyone still close.
• Summons or final thrall wave if you want more bodies.
• Terrain fully active: collapsing ledges, brine surging, psychic feedback.

Round 10 – Climax or collapse

• Last Mind Blast + every remaining control effect.
• If the party has disabled the pool/hub or the golems are battering it, the Elder Brain’s regeneration falters and it becomes more aggressive/melee-focused (or tries to flee via plane shift).
• Clean-up of remaining minions.

Key principles applied

• Action economy is carried by the brain golems + thralls + the two iron golems entering mid-fight.
• Terrain and secondary objectives (pool/hub) keep the fight from being pure “stand and blast.”
• Hits land regularly (AC 30 is high but not untouchable for a high-level party with magic items). SR 34 and regen matter, but volume of attacks, conditions, and objectives matter more.
• No blanket anti-magic, darkness, or constant counterspelling — the Elder Brain uses its natural toolkit (Mind Blast, domination, spells, extract) smartly.
• The golems’ delayed entry creates a visible “we just turned the tide” moment without feeling handed to the party.

Adjust numbers of minions and exact HP thresholds to your table’s power level. If the party is especially optimized, lean harder on the secondary objectives and the golems’ entry timing so pure damage output doesn’t end the fight in three rounds. This should feel like a proper high-level set-piece rather than a miss-fest or a rocket-tag stomp.

Objectives

Layered goals (framework inspired by D&D Has 12 Combat Objectives, Actually — Mystic Arts).

Battlefield features

Interactive terrain and props that make the fight more than a blank grid.

Links

Linked dungeon · Session 302