While similar to 5e's core mechanic, this game simplifies checks significantly. Any time a character attempts a risky action that has a chance of failure, the player rolls a check. Roll 1d20 + modifier and compare against the action’s Difficulty Class (DC).

Either the GM or player of a PC roll checks depending on who is acting in the fiction. If a character has an overwhelming advantage, they can roll 2d20 and take the better. Likewise, disadvantage forces them to roll 2d20 and take the lesser.

Following a check, only a single roll is permitted until circumstances significantly change.

The DC is determined by the GM and based on the difficulty of the action; it can either be static (based on an obstacle) or opposed (like rolling against another character). You succeed if you meet or exceed the DC. The default DC is 11, and any check that doesn't specify always uses that number. However, the GM may set that target to be anywhere between 5 and 20. The GM may also rule that a task is impossible or so simple that it doesn’t require a check.

Any roll of a 20 on a D20 is considered to be a critical success, automatically succeeding. Any roll of a 1 on a D20 is considered to be a critical failure, automatically failing. These special rolls are particularly important because of their effect on the durability of PC's armor and weapons.

Each check can have modifiers which add or subtract a number to the base 1d20 roll (listed as 1d20 + N). PC checks have ability and proficiency modifiers, which represent their capability. Whenever a PC is proficient, they add their proficiency bonus to checks. Each modifier source is added once per roll.

Any time a saving throw is required (traps, spell effects, environmental threats) treat it as a check with the appropriate modifiers. Some circumstances can cause a check to be rolled at advantage or disadvantage. Many spell effects don't have a save, but rather require a successful magical attack against the target.

Magical attack rolls are rolled by a spell-casting character on 1D20, adding his Intelligence modifier (Scholars) or Wisdom modifier (Zealots) plus his proficiency bonus. The result must exceed the defender's defense. Monsters calculate the defense by adding either their Weak, Normal or Strong modifier (depending on the monster type) to a base of 10. On monster stats in this wiki, that defense rating is called “Resistance” and applies to all spells or spell-like attacks, regardless of type. For spell attack rolls made against a PC or henchman, or NPC with full PC class stats, the defense against a spell attack is calculated as 10 plus one ability score modifier chosen by the DM based on the nature of spell (usually either DEX or WIS, but sometimes others) plus his proficiency bonus if the PC or henchman's class is proficient using that particular ability.