What are all the ways to increase the chance of a critical hit?

Question

A natural 20 is a critical hit. Some builds aim for these crits. But how can a player maximize their chance of scoring a crit?

I know a few, some more reliable than others:

• A champion fighter gets crits on a natural 19-20 (18-20 at level 15).
• A rogue assassin attacking a surprised creature will auto-crit.
• A divination wizard can roll a 20 during a rest and spend it on themselves or an ally for a crit.
• Any advantage of course gives greater chance of getting a 20.

Anything else?

Answer 1

The Player's Handbook lists a few different methods of ensuring critical hits, or at least making them easier to obtain. You mentioned a few of them, but I will include them here as well for completeness.

• Fighter's Champion archetype (p. 72): grants the "Improved Critical" traits at levels 3 and 15, allowing you to critically hit on 19s and 18s respectively.
• Rogue's Assassin archetype (p. 97): grants the "Assassinate" feature, which allows you to critically hit on each successful strike performed on a surprised opponent.
• Wizard's School of Divination (p. 116): grants the "Portent" feature, allowing you to "store" two d20 rolls each day for later use. If one of them is a 20, you can later guarantee a critical hit by you or one of your allies.
• The Advantage mechanics (p. 173): Any situation granting advantage allows you to roll two d20s for your attack, increasing the odds of getting a 20 (and thus a critical hit).
• Striking a Paralyzed foe (p. 291): All hits against a paralyzed creature are considered critical hits if the attacker is within 5 feet.
• Striking an Unconscious foe (p. 292): All hits against an unconscious creature are considered critical hits if the attacker is within 5 feet.

The Dungeon Master's Guide offers another way of achieving similar results.

• The Moonblade legendary weapon (p. 217) : one of the Moonblade's potential properties (they are rolled randomly) can grant critical hits on a roll of 19 or 20.

More recently, Xanathar's Guide to Everything also adds a few ways to improve your odds of critically striking.

• Warlock's Hexblade archetype (p. 55): Through the Hexblade's Curse feature, you can critically strike on a 19 or 20 for one minute against a chosen enemy. At level 14, the Master of Hexes feature allows you to transfer this curse to another target, provided it is within 30 feet.
• The Elven Accuracy racial feat (p. 74): Allows you to reroll one d20 when you attack with advantage using dexterity, intelligence, wisdom or charisma.

Answer 2

One thing that hasn't been mentioned is the halfling's Lucky trait. Since this allows halflings to re-roll any 1s that they get, their chances of getting a critical hit are slightly increased, since any reroll of a 1 is another chance to roll a 20.

And, if you happen to be in a party with a halfling who has taken the "Bountiful Luck" feat from Xanathar's Guide to Everything (p. 73-74), you would get this same benefit:

When an ally you can see within 30 feet of you rolls a 1 on the d20 for an attack roll, an ability check, or a saving throw, you can use your reaction to let the ally reroll the die. The ally must use the new roll.

Answer 3

An additional mechanic that works alongside advantage is the Elven Accuracy racial feat (Xanathar's Guide to Everything, p. 74) for elves and half-elves. One of its benefits is:

Whenever you have advantage on an attack roll using Dexterity, Intelligence, Wisdom, or Charisma, you can reroll one of the dice once.

It lets you re-roll an extra time when you have advantage, which increases your chance of rolling a crit even more.

Answer 4

The Lucky feat (PHB 167):

You have 3 luck points. Whenever you make an attack roll, an ability check, or a saving throw, you can spend one luck point to roll an additional d20. You can choose to spend one of your luck points after you roll the die, but before the outcome is determined. You choose which of the d20s is used for the attack roll, ability check, or saving throw.

It allows you to roll an additional D20 on your attack rolls (as well as several other types of rolls) and pick which roll you want (this also negates disadvantage according to RAW, since you pick which roll). You can do so 3 times between long rests.