List of sources of critical hit threshold reduction

Normally only dice rolls of 20 are a Critical Hit. The following is a list of ways to make critical hits more likely.

Reducing the threshold for Critical Hits

These effects reduce the threshold required for a critical hit by 1.

Equipment

Weapons

• Bloodthirst
• The Dead Shot
• Knife of the Undermountain King (against Obscured targets)

Cloaks

• Shade-Slayer Cloak (while  Hiding)

Armour and headgear

• Covert Cowl (while Obscured)
• Dark Justiciar Helmet (while Obscured)
• Sarevok's Horned Helmet

Consumables

• Elixir of Viciousness

Class features

•  Improved Critical Hit

Guaranteed Critical Hits

There are also several ways to guarantee a critical hit.

• The  Paralysed condition, such as from any of  Hold Person,  Hold Monster
•  Luck of the Far Realms (once per Long Rest)
• Killer's Sweetheart (once per Long Rest after killing a creature)