The Echoing Void

The Loop (Core Mechanic). The Void feeds on repetition. Whenever a creature takes the SAME TYPE of action two turns in a row (attack, cast a spell, heal, dash/move away, hide/defend, use an item, or help/interact), the Void gains 1 Loop Charge. When the Void reaches 3 Loop Charges it immediately releases a Loop Burst (see Actions/effects), then resets to 0. Simply put: if the party keeps doing the same thing, the boss punishes them.

Loop Burst. When the Void reaches 3 Loop Charges, every player makes a DC 16 Wisdom save. On a failure: 4d8 psychic damage, and the creature loses one of its movement, bonus action, or reaction (player's choice) until the end of its next turn. On a success: half damage and no other effect. Loop Charges then reset to 0.

Break the Loop (Weakness). When a creature uses a DIFFERENT action type than it used last turn, it disrupts the recursion. Once per turn, the first creature to do so removes 1 Loop Charge from the Void. Change tactics and the boss gets weaker; repeat yourself and it gets stronger.

Attached Echo. While an Echo is attached to a player (see Summon Echoes), that player takes no immediate damage, but on their turn — after they choose an action — they roll a d6: 1–3 the action works normally; 4–5 the action targets the nearest creature instead; 6 the action targets the player themselves or simply fizzles. An attached Echo remains until removed. REMOVING IT: (1) Snap Them Out of It — an ally uses an action to shake, slap, or shout the host's name and makes a DC 14 Wisdom, Medicine, or Persuasion check; on success the Echo is destroyed. (2) Hurt the Host — an ally attacks the attached Echo; the host takes half the damage and the Echo is destroyed. (3) Self-Clarity — the host uses their action to forcefully break the connection, takes 1d6 psychic damage, and the Echo is destroyed.

Recursive Phases. PHASE 1 (100%–66% HP): the Void uses only Smoke Strike, Repeat After Me, and the Loop economy — no Echoes yet. PHASE 2 (65%–33% HP): when it drops below 66%, it immediately summons 4 Echoes and unlocks Echo Pull and Summon Echoes. PHASE 3 (32%–0 HP): the Void becomes unstable — at the start of each round it gains 1 Loop Charge automatically, and Echoes now attach when only 2 reach a player instead of 3.