I’ve created a coastal adventure and my players are having some run ins with a monstrous shark! 

I wanted to create some potential for some limbs to be lost during combat with the shark.

Would appreciate some guidance on how/when to have players lose a limb in combat? 

thanks!

The DMG has some guidelines for this in chapter 9. They suggest checking for lingering injuries on a critical hit, when a creature falls to 0, or fails a death save by 5 or more.

Sword of Sharpness does it if:

1) You get a natural 20 on a to hit AND  2) You then roll another natural 20.

I do not think a Shark should be better than a magical sword of Sharpness.

But I do agree that a failing a death save by 5 or more could do it

Realize that you could effectively kill a character if you do this and they don’t have access to regeneration or some kind of magical prosthetics. Most melee build are completely shattered with only one arm. And pretty much every character is wrecked by losing a leg. 

Quote from Xalthu >>

Realize that you could effectively kill a character if you do this and they don’t have access to regeneration or some kind of magical prosthetics. Most melee build are completely shattered with only one arm. And pretty much every character is wrecked by losing a leg. 

 Both the Eberron book and Tasha's include the Prosthetic Limb magical item; it's a common magical item, and could subsequently be easily incorporated into most campaigns without much fuss.

As for potentially killing the character, healing spells should cover the wounds and bleeding. Equipping them with a magical prosthetic limb - a leg, in your example - would put them right back into fighting shape. They'd also now have a cool magically-created prosthetic leg to show off and look badass with.

A critical hit from a shark' bite could dismember if you want. Or have  Constitution saving throw to do so whenever it deals max damage.

One way or another, it should be rare, you don,'t want more than half the party missing one or more limbs after a ramdom encounter with sharks.

Quote from Chimpbot2099 >>

Quote from Xalthu >>

Realize that you could effectively kill a character if you do this and they don’t have access to regeneration or some kind of magical prosthetics. Most melee build are completely shattered with only one arm. And pretty much every character is wrecked by losing a leg. 

 Both the Eberron book and Tasha's include the Prosthetic Limb magical item; it's a common magical item, and could subsequently be easily incorporated into most campaigns without much fuss.

As for potentially killing the character, healing spells should cover the wounds and bleeding. Equipping them with a magical prosthetic limb - a leg, in your example - would put them right back into fighting shape. They'd also now have a cool magically-created prosthetic leg to show off and look badass with.

 That’s why I specifically mentioned magical prosthetics more than 2 years ago when I made the post. Before Tasha’s came out, when Eberron was the only source for them, and not all campaigns are willing to use items from other worlds.

I'm a fan of having lingering wounds as a possibility, but they shouldn't be too easy to acquire, and I'm personally not a fan of the suggestions in the DMG; while the effects are fine, I don't like simply tying them to rolls, as there's too much potential for a player to feel like you're punishing them for being unlucky, which already sucks. Plus you essentially have to roll on a table before you can even begin describing the attack properly, as it won't make a lot of sense for a player to lose an eye after an enemy attacked their leg.

For example, if your shark hits the same player for a second turn in a row with its bite, then you might describe it as biting deep into the flesh of the arm, and the water is turning red with blood. Mechanically you may rule they are grappled and can't use the arm until the grapple is broken. This should be enough to telegraph that the player's arm is in real danger, and gives the party a round to try and get them free. Depending on the damage the arm may still be useless, but the difference between saving it and losing it is that a mauled arm can be healed much more easily than a missing limb can be replaced.

I much prefer this kind of situational/narrative handling of it to trying to devise a simplistic rule which is what I feel the DMG does. Again though, the effects themselves are fine, by all means use the table for those, but I'm not a fan of rolling it as described personally. Also, if the shark does get a person's limb, please, please, please start with the line "So the good news is the shark no longer has you grappled…". 😈

One thing I would say; while temporary injuries should be fine in most groups, you should discuss with your players before lopping parts off of any of them. This is a good topic for a session zero, but it's also something that you could just raise between sessions, as not everyone is going to be happy with the possibility of disfigurement, body horror and the like. If you want to spring it as a surprise, be ready to make it easy to replace any missing limb(s) as your players may not be okay with being stuck with an injured character for any length of time.

I tend to lean towards only dishing out temporary injuries, and usually these are karmic in nature; for example, a player jumps from a height I made clear was dangerous and then whiffed their Acrobatics check, or the party made camp somewhere I was clear was dangerous etc., enough to (maybe) teach a lesson. "Permanent" injuries I will dish out only when it makes for a good story, and when I know there's a way to fix it later.