Poison
The effects of poison are some of the most nefarious and deadly in the game. The typical poison attack only does damage in the first round, but the effect of being poisoned can linger for some time, causing nasty trouble for our adventurers.
The typical poison attack, let’s say the bite of a terrible spider, starts with the spider’s roll to hit. On a successful hit, the target takes the bite damage and must make an additional CONSTITUTION Saving Throw against the effect of the poison. The difficulty number of that particular poison will always be called out in the description of the monster.
On a successful Saving Throw the target takes no additional damage nor suffers any ill effect.
On a failed Saving Throw the target takes any additional damage listed in the text and becomes “poisoned”. A poisoned character is queasy and dizzy and is at Disadvantage on all rolls — Attack Rolls, Ability Checks, and Saving Throws. Disadvantage means that a player rolls a d20 twice and uses the lower of the two numbers to calculate a success or failure.
Players typically can retry their Saving Throw again at the end of each of their turns to end the effect. But remember the Disadvantage. Because of this, the queasiness can last a long time for unlucky players. Every poison is different, so make sure to read the description carefully.