Paralisados e Inconscientes produzem crits automáticos
Com a ressalva de que você deve estar dentro do alcance, no entanto.
Do Manual do Jogador -
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Paralyzed
A paralyzed creature is incapacitated (see the condition) and can’t move or speak.
• The creature automatically fails Strength and Dexterity saving throws.
• Attack rolls against the creature have advantage.
• Any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.
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Unconscious
• An unconscious creature is incapacitated (see the condition), can’t move or speak, and is unaware of its surroundings.
• The creature drops whatever it’s holding and falls prone.
• The creature automatically fails Strength and Dexterity saving throws.
• Attack rolls against the creature have advantage.
• Any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.
Além disso, como observado por @Allan Mills (Obrigado!), Um ladino de arquétipo assassino também receberá a crítica automática com acertos em oponentes surpresos, começando no nível 3rd.
Assassinate
Starting at 3rd level, you are at your deadliest when you get the drop on your enemies. You have advantage on attack rolls against any creature that hasn't taken a turn in the combat yet. In addition, any hit you score against a creature that is surprised is a critical hit.