Quick answer: The Physicist is the Underpass Resonant fight at the Spire summit / Astral Plane. The objective Kill the Underpass Resonant opens after Recursions and Iterations; the file sits on the Spire table. You need Shift and Gravity Anomaly. Collect three sequential Astral Keys from glass boxes (not on the minimap), then fight through AoE chase explosions, aerial projectile volleys, ground sweeps, spike waves, and orb splits. Choose Spike or Astral Rebuke; also Untapped Golden Earrings recipe and Astral Reconfiguration trophy.
Where is the Underpass Resonant / The Physicist?
Underpass Resonant access is at the Spire summit on the Astral Plane path. Pick up the Kill the Underpass Resonant objective after Recursions and Iterations from the file on the Spire table. Boss location framing also lives on resonants and fight habits on boss tips. House-side Fault work that often sits near this stretch is on House in Distress.
What abilities and climb priorities do you need?
Confirmed prerequisites: Shift and Gravity Anomaly. Bring Blunt for the Eskil Hiss Pursuer mini-boss on the climb. Prioritize Hiss Freighters and shove enemies off the wall when the geometry allows — the climb is as much vertical crowd control as a boss approach.
Where are the three Astral Keys?
Three sequential locked doors each need an Astral Key. Keys are not marked on the minimap; they sit in glass boxes. Order matters because each door unlocks the next stretch.
- Key 1 — Drop to lower platforms beside the door, follow the desks/office trail; glass box on a table
- Key 2 — Far path; after cubes you go upside-down; key on a bed in the iron cube room; Health Upgrade Point 1/3 yellow cat dispenser nearby
- Key 3 — Left drop path into an inverted corridor; key on a desk/table; four chests in the area; then residence with Letter from Howie, Physicist’s Log #7, and a glowing mirror that starts the fight
How do you beat The Physicist?
Confirmed tells: AoE chase explosions; aerial projectile volleys (circle-sprint); ground sweep (jump); spike waves; boss splits into orbs (focus the orbs); final phase mixes two orbs plus the boss — do not get greedy on damage windows. Ability toolkit context: abilities.
| Threat | Response (confirmed) |
|---|---|
| Aerial projectile volleys | Circle sprint |
| Ground sweep | Jump |
| Orb split phases | Focus orbs; final phase two orbs + boss |
What rewards does The Physicist drop?
Choose Spike (summon/direct knockdown, Astralized) or Astral Rebuke (homing ground eruption, Lifted + Astralized). Also confirmed: Untapped Golden Earrings recipe and the Astral Reconfiguration trophy. Artifact priority context: best artifacts. Quest gate context: Recursions and Iterations.
Spike or Astral Rebuke — what is confirmed?
Confirmed choice framing only: Spike summons/directs knockdown and carries the Astralized tag; Astral Rebuke is a homing ground eruption tagged Lifted + Astralized. This dossier does not invent a universal “always pick X” meta beyond those tooltips. Pair the choice with your Lifted / Astralized build needs and Mold or crowd habits already covered on abilities pages.
Astral Key FAQ (minimap and glass boxes)
Why can’t I see Astral Keys on the minimap? Confirmed: they are not minimap-marked. Search glass boxes along the desk/office trail (Key 1), the upside-down iron cube room bed (Key 2), and the inverted corridor desk/table (Key 3). Key 2’s area also hosts Health Upgrade Point 1/3 via a yellow cat dispenser nearby. Key 3’s stretch includes four chests, then the residence with Letter from Howie, Physicist’s Log #7, and the glowing mirror that starts the fight.
Climb and mini-boss notes before the arena
Shift and Gravity Anomaly are the documented ability gates. Blunt matters for the Eskil Hiss Pursuer mini-boss on the climb. Priority-target Hiss Freighters and shove threats off the wall when the Spire geometry allows. Those climb rules are separate from House in Distress Electrokinesis work even when both threads sit after Recursions and Iterations.
Final-phase greed is the most common documented fail pattern: when two orbs and the boss share the arena, focus orbs first and take short punish windows instead of ignoring splits. Circle-sprint aerial volleys and jump ground sweeps remain the confirmed movement answers for those tells. Spike waves are a separate tell in the same fight vocabulary — treat them as their own dodge window rather than conflating them with ground sweeps.
Untapped Golden Earrings recipe and Astral Reconfiguration trophy sit beside the Spike / Astral Rebuke choice as confirmed post-fight payouts. Crafting the earrings still happens through the usual Untapped Artifact / Gap path once you hold the recipe — this page only confirms the recipe unlock, not invented craft costs.
This page stays on confirmed Astral Key routes, climb gates, fight tells, and reward choice. It does not invent DPS rotations, hidden fourth keys, or unstated difficulty modifiers for the Underpass Resonant.
Related: resonants · boss tips · abilities · Recursions and Iterations · House in Distress · best artifacts.