Desert Crossing

Rules for foot travel across the open flats of the Hellcatch Valley — and
Nuxan’s deep desert generally — where purple worms hunt by ground-rhythm.
Crawlers bypass all of this (see Rig Rules). Self-contained.

The Threat

Purple worms (standard stat block, CR 15) sense vibration through tremorsense
and are drawn from a distance to the steady cadence of a natural walking gait or
a rolling wheel. On the open flats, a party on foot walking normally draws one to
itself with every step. A CR 15 worm against a low-level party is not a fight —
it’s a disaster to survive.

Three things keep people alive:

• Cities. Constant industrial noise floods the ground and worms won’t
  approach it. Settlements sit on effectively safe ground; walking in and
  immediately around a desert city is fine.
• Rigs. Crawlers run subsonic gear that scrambles worm tremorsense. Rig
  travel across the flats is safe barring gear failure — which is why reaching or
  owning a rig is the real key to leaving on your own terms.
• The Weathered. Deshretu’s survivors (see Deshretu) walk the flats in
  a trained, broken-cadence gait that never settles into a rhythm a worm can read.
  Earned knowledge, taught not bought — an outsider doesn’t have it.

The Gate

A party with no rig, no technique, and no Weathered guide cannot cross the open
flats on foot. They don’t get a check — natural walking draws a worm, full
stop. Leaving Bassuras overland requires acquiring one of the three: the
technique is a relationship (the Weathered), the rig is debt or ownership. Until
then the desert is the wall.

Crossing on Foot

Once the party has the technique or a guide, foot crossing is possible but stays
dangerous. Resolve as repeated group checks, never one roll.

Cadence. One group Wisdom (Survival) check per leg — a leg being roughly
a half-day of open-flats travel (set granularity to taste: per watch, per terrain
change, per half-day). A full crossing is several legs. The repetition is the
point; the crawler is meant to look better with every check.

The check. Everyone rolls Survival. Apply the group-success rule and count
individual failures:

• Half or more succeed → the leg passes. If anyone failed, it’s a
  near-miss: distant worm-sign, ground lurching underfoot, a spent resource
  (water, a spooked mount), lost time. No attack — the steady walkers covered the
  broken gaits. Narrate that the thing is out there.
• Fewer than half succeed → a worm is drawn. It surfaces on the party. Run it
  as a catastrophe to escape, not a winnable fight (below).

Baseline DC 12 — clear day, open flats, unladen, technique known.

Modifiers

Two buckets, kept separate on purpose. Conditions move the DC; walker state
grants advantage/disadvantage. (2024 disadvantage doesn’t stack — pile every
factor onto adv/disadv and most are wasted. Route conditions through the DC so
they register.)

DC adjustments — the crossing:

Condition	DC
Baseline — clear, open flats, daylight, technique known	12
Sandstorm or high wind	+3
Deep flats, far from any city-noise	+2
Worm-active season / recent tremors	+2
Night (worms nearer the surface)	+2
Nearing city-noise, ruins, or bedrock (dead ground)	−2 to −5

Advantage / disadvantage — the walkers:

• Weathered guide setting the pace: advantage. Survivable, never safe — the
  guide still rolls, the party can still fail.
• Heavy armor: disadvantage.
• Encumbered, or hauling noisy/heavy cargo: disadvantage.
• Forced march / moving fast: disadvantage.
• These don’t compound — any one imposes disadvantage, the rest are flavor. Which
  is why the real choice is leave light or don’t leave.

Exhaustion rides on top via the normal rules (forced march, heat, no water) —
−2 per level to all d20 tests in 2024. An exhausted armored walker eats
disadvantage and a stacking flat penalty on the same check, and degrades each
leg; armor and encumbrance accrue it faster. Night crossings cut the heat
pressure but raise the worm risk — a real tradeoff, not a strictly worse option.
Don’t fold exhaustion into disadvantage; let it be its own penalty.

When a Worm Is Drawn

A CR 15 worm kills a low-level party in a straight fight, so don’t run one. It
surfaces at distance and telegraphs; the party gets a beat. Escape means breaking
the rhythm it locked onto — go still, reach dead ground (bedrock, ruins,
city-noise), or reach a rig and its deterrent. A worm that misses is slow to
re-acquire. Losing the mounts, the cargo, or a rig to buy the escape is the
intended price. A TPK should come from compounding bad calls, not one failed
group roll.

Texture

Occasionally surface a worm on a clean leg — breaching on the horizon, pacing
the group for a mile, taking a lone pack animal and going back down. It’s a
hunting animal, not a skill tax. Once or twice a campaign, not per crossing, or
it stops meaning anything.

Quick Reference

• No rig, no technique, no guide → can’t cross on foot. Worm, no roll.
• Otherwise: group Survival per leg, DC 12 ± conditions, adv/disadv from state.
• Half+ succeed = pass (near-miss if anyone failed). Under half = worm surfaces.
• Worm = escape scenario, not a fight.