New Crit Rules for 5e

The standard rule for crits in D&D 5E is simply roll double the dice you normally would. In the DMG there is a table to lasting wounds that can leave heroes with crippled or even lost limbs eyes and worst by even a small scratch if it crits. I've used both and honestly the lasting wound table on every critical gets pretty messy after a while and just doing extra damage can get boring once you're five or so levels into a campaign.  After so time I worked out a system that has a chance as horrible limb losing wounds, but they should only happen on attacks that would actually be capable of it. More so I was never a fan of all damage types having the same outcome when a crit with a hammer should feel completely different from a crit with a blade.  In the end I came up with this table and a save that scales based on damage.  This way minor damage doesn't have major effects (though even minor wounds can be game changers in the short run) and even some options to get rid of all but the worst wounds without needing magic in your games.

Save VS Wound: When hit with a Critical Attack you must make a Con save equal to half the attack's damage or 5 whichever is higher. A character cannot fail this save by more than half the damage taken.

Save	Minor Scar
Fail	Minor Wound
Fail by 5+	Medium Wound
Fail by 10+	Major Wound
Fail by 15+	Grievous Wound

Wound Level	Piercing	Slashing	Bludgeoning	Magic
Minor Wound	Precise Strike: The attackers adds their proficiency bonus to the damage taken.	Burning Cut: Your next Action is made at disadvantage.	Sundering Hit: You drop a single held item, player's Choice.	Powerful Casting: The attackers adds their proficiency bonus to the damage taken.
Medium Wound (Treated with  either a short rest and a DC15 Medicine check or a first level healing spell.)	Impaled: One of your limbs is run through and unusable until treated.	Open Cut: After each action you suffer d4 bleeding damage until treated.	Fracture: All actions are at disadvantage until treated.	Mana Scar: Future magical attacks from the same caster have advantage until treated.
Major Wound (Threated with either a long rest and DC20 Medicine Check or a 3rd level healing spell)	Run Through: Take damage equal to the attacker's proficiency bonus each time they take an action, if the target is doing nothing this is instead per hour until treated.	Deep Gash: One of your limbs in unusable until treated. Roll a d6  (1-3=a Leg, 4-5=off hand, 6=main hand) If that limb is already affected nothing happens. If a leg is already affected there is a 50% chance nothing happens	Shattered Bone:  One of your limbs in unusable until treated. Roll a d6  (1-3=a Leg, 4-5=off hand, 6=main hand) If that limb is already affected nothing happens. If a leg is already affected there is a 50% chance nothing happens	Mana Vulnerability: Further attacks from the same caster have advantage and you suffer disadvantage against saves from that caster until treated.
Grievous Wound (Treated with a week's rest and DC20 Medicine Check or a casting of Regeneration or higher)	Serious Organ Damage: Your maximum hit points is reduces by an amount equal to the attacker's proficiency bonus each day until treated or death. During Treatment this damage is halted.	Limb Loss: One of your limbs is severed Roll a d6  (1-3=a Leg, 4-5=off hand, 6=main hand) If that limb is already affected nothing happens. If a leg is already affected there is a 50% chance nothing happens To allow the limb to be healed the lost limb must be preserved by magical means such as Gentle Repose.  If not the limb is replaced with a prosthetic and have learned to adapt taking a month.	Crippled Limb: One of your limbs is too badly crippled for all but the strongest of magic. Roll a d6  (1-3=a Leg, 4-5=off hand, 6=main hand) If that limb is already affected nothing happens. If a leg is already affected there is a 50% chance nothing happens	Lasting Effect: You maximum hit points is reduced by the amount of damage taken.

New Feat: Duelist

You gain +1 Dex and can use Dexterity in place of Constitution when saving against a critical wound.