Quick lookup for common D&D 5e rules
Obstacles provide protection from attacks and effects
Grab a creature using the Attack action
Push a creature prone or away from you
Attack with two light weapons
React when enemies leave your reach
Obstacles that slow movement
Become unseen and unheard
Maintaining focus on a spell
Fighting for survival at 0 HP
A brief period of rest (1+ hours)
Extended rest period (8+ hours)
Taking damage from a fall
Running out of air
Gain advantage by positioning
Prepare to act later with a trigger
Aid another creature's check or attack