Rules variants being used (as listed in the PHB and DMG)
Variant Humans (PHB) – Humans may choose to either have +1 to all stats, or +1 to two different stats + a feat + a skill proficiency
Feats (PHB) – Feats are fully usable by players
Healer’s Kit Dependency (DMG 266) – Players cannot use Hit Dice to heal after a short rest unless someone uses a healer’s kit to bandage and treat wounds.
Slow Natural Healing (DMG 267) – Players don’t automatically regain hit points at the end of a long rest. Players can use Hit Dice after a long rest without using healer’s kits.
Hitting Cover (DMG 272) – If a ranged attack on someone in cover misses by an amount equal to or less than the cover bonus, the attack hits the cover instead.
Knocking someone unconscious (automatic stabilization) Instead of the standard rules, where players and enemies choose whether to knock someone unconscious or mortally wound them when they reduce their health to 0, someone must state that they are attacking to knock unconscious before the blow, and it applies disadvantage. The blow still causes full damage, if the creature is brought to 0, then they are instantly stable.