We are implementing a system of critical successes and failures on non-attack rolls using the Fates and Fortunes deck by Nord Games. When a player rolls a natural 20 on any d20 check (other than an attack roll - such as skill checks, saving throws, etc.), they draw a Good Luck card from the deck. They read the effects aloud and keep the card face-up in front of them until they choose to use it.
When a player rolls a natural 1, they instead draw a Bad Luck card. After reading the effect aloud, they pass the card to the DM, who will determine when and how it affects them as an unexpected setback in the future.
Some Good Luck cards grant minor fortuitous circumstances that allow players to influence the game world to their advantage. However, whether these effects are feasible or applicable in a given situation is ultimately at the DM’s discretion.
For example, the Damaged Goods card, which allows a player to guarantee that a merchant has an item they need, only works if it is reasonable for that merchant to have it in stock. The DM determines what is plausible based on the merchant’s trade and location. For instance, an armorer might reasonably have a suit of plate mail (yes), but a Staff of the Archmage (no) would be far beyond their usual inventory. A set of elven mithril chainmail (possibly) could be available, but it would be rare and extremely expensive.
Bosses, solo monsters, and certain NPCs may be immune to some of the effects of these cards. In such cases, if a player attempts to use a card against an immune target, the DM will simply state that the card has no effect. The player retains possession of the card and may use it again later—it is not wasted.
Fortune Cards that grant additional damage or effects in combat cannot be combined with the effects of a Critical Hit. If a player wishes to use a card that increases damage, applies conditions, or alters combat effects, it must be declared before the attack roll, and if a critical hit is scored, the card's effects are nullified and remain available for later use.
If a Fortune Card grants a reroll, it cannot be combined with Heroic Inspiration to allow yet another reroll. Players may only benefit from one reroll effect per action, ensuring that fortune and fate remain balanced in gameplay.
Fortune Cards are only granted based on the initial roll of the die. If a player has a reroll from a Fortune Card, Heroic Inspiration, or another source, the original roll still determines whether a card is drawn. If a player rolls a natural 1 and then rerolls, they still receive a Bad Luck card. Conversely, if they roll poorly but reroll into a natural 20, they do not receive a Good Luck card—only the first roll of the die matters for drawing Fortune Cards.