Whenever a crawler tries something risky or interesting, the player makes a Check: roll a d20, add a Stat Mod and (for a Skill) the Skill’s Rank, and compare the total to a Difficulty set by the GM. Meet or beat it and you succeed. The GM never rolls d20s; Mobs and NPCs are represented by Difficulties instead.
The five Stats
| Stat | What it covers |
|---|---|
| Strength (Str) | Physical power and brawn |
| Intelligence (Int) | Smarts and knowledge; sets your Mana |
| Constitution (Con) | Toughness and stamina; sets your Health |
| Dexterity (Dex) | Agility and coordination; used to Evade |
| Charisma (Cha) | Presence; persuading, coercing and attracting viewers |
Setting the Difficulty
Every Difficulty starts at 10 and gets harder the deeper you go, because the Floor Number is added in:
| Check | Difficulty | Examples |
|---|---|---|
| Unopposed Skill Check | 10 + (Floor × 2) | Climbing, Dumpster-Diving, Endurance |
| Opposed Check | 10 + antagonist’s Stat Mod + Floor | Fighting a Mob, persuading an NPC |
| Stat Check | 10 + Floor | Forcing a stuck door, resisting alcohol |
The GM can always set a different Difficulty when that makes more sense.
Advantage and Disadvantage
With Advantage, roll two d20s and keep the higher; with Disadvantage, keep the lower. One of each cancels out, and extra sources don’t stack: you never roll more than one extra die. If you try an Attack or Utility Skill you have no Ranks in, you roll with Disadvantage and add only your Stat Mod.
Degrees of Success and Failure
| Result | When | What it means |
|---|---|---|
| Critical Hit | Natural 20 | The best possible result. Attacks roll double base damage dice. |
| Amazing Success | Beat the Difficulty by 10+ | Extra impact. Attacks add damage equal to the Floor Number. |
| Standard Success | Meet or beat by 0–9 | You succeed. Ties go to the crawler. |
| Near Miss Fail | Fail by 1–2 | So close; in combat, allies can Intervene. |
| Standard Fail | Fail by 3–9 | A normal Failure; the GM may let you fail forward. |
| Major Fail | Fail by 10+ | Failure with a consequence; no retrying that Skill this scene. |
| Critical Fail | Natural 1 | The worst possible outcome. |
Party Checks
When the whole party acts together, everyone rolls. If half or more succeed, the party succeeds. An Amazing Success or better can turn one teammate’s failure into a success; a Major Fail or worse can turn one success into a failure.
Source: Rules for Survival, pp. 12–15 and 30–31. Try it with the dice roller.