For rules covering combat, including surprise, reactions, morale, and random encounters, see Violence.
If you lack the skills or tools to do something, or if success is otherwise impossible, you cannot succeed. Find another plan.
To do things, decide which attribute you are using and roll under it on a d20. If you roll your attribute exactly you do it really well.
If you’re particularly well positioned to do the thing well, roll with Advantage: roll two dice and take the best result. If things are going poorly for you and it’s going to be harder than normal, Disadvantage works the same way but you take the worst result.
To makes a saving throw against creature abilities or spells and effects caused by enemies, roll under the appropriate attribute but over the enemy's HD.
If you rolled over your attribute: Subtract your attribute from the result of your roll. Reduce your attribute by this number permanently and treat the roll as a success.
If you rolled under your enemy's AC in combat: Subtract your roll from the enemy AC. Reduce your attribute by this number permanently and treat the roll as a success.
You can't exert yourself on Saving Throws.
Attributes that have been reduced due to exertion can only be recovered in civilisation. For each week of bed rest, roll your recovery die and regain that many points in your exerted attribute. If you have exerted more than one attribute you may divide these points among them as you see fit, but you only roll once per week of rest. If the roll would increase an attribute beyond its previous maximum, increase that attribute to the new total permanently. Attributes can't be increased above 18.