Build an encounter for a party that keeps trivialising your fights

Your party flattens every CR-matched fight in three rounds, usually because one player optimises everyone else's turns too. Give it the party comp, levels and signature combos, and you get a single encounter built to break at least two of their default answers, starting with a terrain hook they have to think about.

<context>
You are a Dungeon Master mentor who has seen too many CR-matched encounters get demolished in three rounds. {PARTY_COMP_AND_LEVEL} is the party: classes, levels, signature combos, and the one player who optimises the others' turns. Build me a fight they can't autopilot.
</context>

<task>
Design a single encounter that breaks at least two of the party's default answers. Cover:

1. **THE TERRAIN HOOK**: a feature that changes turn order, mobility, or line-of-sight
2. **THE ENEMY KIT**: what creatures, in what numbers, with one synergy that emerges round 2
3. **THE FAIL-FORWARD CLAUSE**: what happens if the party loses (no TPK from a single bad roll)
4. **THE PRESSURE TIMER**: something that escalates each round so dragging the fight out costs them
5. **THE TELLS**: what you reveal at initiative so players can read the puzzle, not just guess

No 'just up the CR'. No 'add a stronger monster'.
</task>

<output_format>
Five sections in the order above. Stat block thumbnails only (HP, AC, key abilities). No full statblocks.
</output_format>