To balance play between classes, all active rolls--not just skill and combat--are subject to a chance of critical failure and critical success. Casters will roll an additional d20 before casting a spell; a 1 is critical failure, a 20 is critical success. A critical failure usually results in simple spell failure, with a loss of components in the case of powders or liquids or if the component is very fragile, a critical success might significantly increase spell duration, intensity, or range, but all successes and failures will be adjudicated on a case-by-case basis. It is not necessary to roll for cantrips and orisons.

The Survival nonweapon proficiency must be applied to a specific environment. The character has basic survival knowledge for that terrain type. Additional proficiency slots can be used to add more types of terrain.

A character skilled in survival has a basic knowledge of the hazards he might face in that land. He understands the effects of the weather and knows the proper steps to lessen the risk of exposure. He knows the methods to locate or gather drinkable water. He knows how to find basic, not necessarily appetizing, food where none is apparent, thus staving off starvation. Furthermore, a character with survival skill can instruct and aid others in the same situation. When using the proficiency to find food or water, the character must roll a proficiency check. If the check is failed, no more attempts can be made that day.

The survival skill in no way releases the player characters from the hardships and horrors of being lost in the wilderness. At best it alleviates a small portion of the suffering. The food found is barely adequate, and water is discovered in minuscule amounts. It is still quite possible for a character with survival knowledge to die in the wilderness. Indeed, the little knowledge the character has may lead to overconfidence and doom!

Here are the environments available. Note that these are broader definitions than the Complete Ranger's Guide.

• Aquatic. This terrain type includes all areas consisting primarily of water, such as lakes, oceans, rivers, islands and coastal regions.

• Arctic. This includes any region covered with ice and snow where winter temperatures rarely rise above zero degrees. The South Pole is good example of arctic terrain.

• Desert. This includes any barren, flat areas covered with sand or hard-packed earth. Desert climates are frequently extremely dry and hot, with summer daytime temperatures commonly in excess of 100 degrees, followed by much colder nights, but there are cold deserts too (the Gobi, the Great Basin) where the main form of precipitation is snow or fog. Vegetation is sparse, with special adaptations. Much of a desert may be unsettled or unexplored.

• Forest. This category comprises any woodland areas in temperate, subarctic and subtropical climates. Forests abound with a variety of animal species, and vegetation flourishes.

• Mountain/Hill. This category includes highlands, often wild and rough, which may or may not be forested, and terrain consisting of high rocky peaks, typically 4,000 feet or more above sea level, with sparse vegetation, severe slopes, and jagged cliffs. Subtropical to subarctic climates are typical, though a wide range of temperatures is possible.

• Jungle/Swamp. These are lands (including rain forests) overgrown with dense vegetation and trees, and teeming with animal life. This includes bogs, marshes, and other low elevation areas with standing water or waterlogged soil. Many species of reptiles, birds, and insects live in these regions. Vegetation grows in abundance. The climate may be oppressively hot and humid or cold and misty.

• Plains. These are flat areas with stretches of low rolling land, including pastures, meadows, fields, and farmlands. Grazing animals are common here. Such regions are usually covered with grasses or scrub vegetation and are usually temperate in climate.

The Foraging, Fishing, and Hunting nonweapon proficiencies are also environment specific.

Although any character can try to locate a small amount of a desired material, such as food, a branch suitable crafting into a club or bow, enough kindling to start a fire, a medicinal herb, or a component required for a spell, the chances of success without Foraging proficiency are negatively modified, sometimes heavily so. However, in the environment they are familiar with, the proficient characters' chances of success are the same as described in the PHB.
Available terrains are:

• Coastal
• Terrestrial Aquatic (Lake and Streamside only)
• Desert
• Forest
• Mountain/Hill
• Jungle/Swamp
• Plains

The player can select:

• Terrestrial--Rivers and Brooks (Moving Fresh Water)
• Terrestrial--Lakes and Ponds (Still Fresh Water)
• Coastal--Beaches and Tide Pools
• Oceanic--The Open Ocean

Access to these environments may be restricted depending on character history. Full utilisation may be equipment dependent.

Hunting terrains include knowledge of lakes and streams that are used as water sources by the target animal.

• Desert
• Forest
• Mountain/Hill
• Jungle/Swamp
• Plains