Incarna reflected the “gritty realism” (see 5th Edition DMG p.) perspective and lethality missing in the common tropes most often presented in ©Dungeons and Dragons™. The HP and AC mechanics were really no more than an endless pursuit of pluses and adjustments. With 5th edition, many of these approaches are defined variants and now work well in a balanced DnD system. The “Incarna D20 Branch” (originally begun in 08/2015 – see original work & original announcement) is a branch of the Incarna game which incorporates D20 rules with a set of custom guidelines (essentially a “home brew“) to produce a custom variant. Incarna is proud to also stand as a still fully independent and unique approach (“Incarna Core”) among many independent game builders.
Because of the normal short and long rest times’ ability to have a character regain their spells so rapidly, magic was nerfed so that many spells that used to be fail once/failed for the duration are now fail once/re-check each round. The default of empowering magic removes the “check each round” aspect of spells. Once a spell save is failed, it is failed for the duration.
The system relies on a lot of randomly checked outcomes. This has a tendency to slow the game down (purposely not present in the Incarna Core versions), so the D20 variant adopts this rule variant (per DMG) to denote where the average for a randomly checked result is used in place of the check. There are ways around this, depending on how players apply Essence options to their characters.
A short rest is a full night of rest. A long rest is a full week of rest. The normal Survival Rules for Incarna apply otherwise.
A: Yes – A DM can easily apply or or not any of the Incarna variant rules to purchased supplements.