Hey, I'm pretty new to Dming and i have a slight dilemma. Our friend group has always had it so druids get pets/familiars. idk we all just wanted that. Now one of my players wants a stunted copper dragon wyrmling as hers. How do i make that balanced? Health wise, we always just do that your pet's health is half of yours, rounded down. But that thing is still too much. 

Too much as in, the breath weapons are overpowered for 2nd level. Normally people in our group choose like a wolf or something that really only has one attack and does't do too much damage. Im Just not sure how to make her happy without making everyone else feel like i favored her or something. 

Not sure you can. Having a dragon as a pet seems to defeat the idea of having a pet or familiar (which are normally regular animals) and seems to be a stretching of the rules without knowing how it was justified (did someone else have a different mythical creature?).

Druids, using the Wild Companion feature, usually do have a pet/familiar. it is limited, within the rules, tot he creatures available through the find familiar spell. So  bat, cat, crab, frog (toad), hawk, lizard, octopus, owl, poisonous snake, fish (quipper), rat, raven, sea horse, spider, or weasel. I have seen historic additions such as Wolf, Fox, Coyote, and the like, and in older campaigns when they were first introduced, faerie dragons, but I would never have allowed a true dragon of any sort to be a pet.

Seems solvable. The dragon is "stunted," so you can either scale back the breath weapon to a level that you are comfortable with, or limit its usage somehow by making it erratic or unreliable. Maybe each attempt requires a d6 roll first and will only happen on a roll of 5 or 6 or the dragon just burps up some harmless gas or acid slobber that adds a small amount of acid damage to its next Bite attack. 

I like that. I'll have a conversation with her about scaling it back a bit and see what happens. thank you 

is it a pet, a companion, or a familiar? They’re not all the same thing. A pet is basically just an animal, maybe a well trained animal, but an animal nonetheless. A companion is a supercharged pet like Rangers get, and a familiar is a magic pet like wizards get. So which is it?

Even something like a wolf as nothing more than a free pet is kinda unbalanced since the Druid is one of the strongest classes as is. You would have to nerf a wyrmling hard to make it be anything close to “balanced.”

From the sound of things, it seems more along the lines of "the druid brings an animalistic party mascot to the group" as part of their deal. Which is just fine since it sounds like the group has always been cool with this idea. The issue is just scaling the monster to a space that the DM is comfortable with. 

I'd homebrew a creature, and the breath weapon would be in line with whatever the other players pets can do.  Acid, I'd say 1 d6 maybe, in a 10 foot cone at most.  Bite and claw would match what maybe a bear or wolf could do.  Essentially I'd make it the same as every other option (wolf, bear etc) but looks like a dragon.  If the player protests too much and kind of demands a seriously OP "pet" I would advise they can take the standard pet model I offered or have none.  As a few have said, balancing the pet, since it's not even really following rules, is of utmost importance.  Otherwise you would have to upscale your encounters to the point they could easily TPK if a couple rolls went against the group.  There is a fine line between letting your players have fun stuff and letting them have stuff that plain breaks the game.

GM: You have a pet stunted dragon. Now, pets are noncombat features. During a combat it will be assumed to be either hiding or having its own combat just off-camera and not controbuting to the main combat. If you want your pet to take part in the main combat then you need to make your character a summoner of some kind, or a beast master ranger, or something like that. No, I'm not giving you a combat pet for free - that wouldn't be fair to the people who are playing summoners and who have to spend resources to get their combat allies.

As a related aside, when it came to mounts I basically told everyone that their mounts would be a Warhorse or equivalent.

One person wanted a wolf, so we used a Warg stats.

One wanted a drake, so we used Warhorse stats and reskinned the kick for a bite.

One wanted a pony, so we gave it Warhorse stats so it didn't just die.

The others had find steed and a magical rock, so they were all good.

At any rate, your best bet would be to make a generic "pet" statblock and say "You can skin it however you want, it has these stats" and then keep it as a thematic item.

My rule of thumb when it comes to things like this is a "reskin". Take the stat-block of an actual familiar, let's say a raven, have the player use that when it comes to combat. But the familiar looks like a stunted copper dragon wyrmling.

If they want to have their familiar get stronger, make them work towards it. Perhaps they need to make an arcana skill check to heal/empower the wyrmling. If they eventually want to use the  stat-block of a copper dragon wyrmling, you can have them use an appropriate level spell-slot to temporarily empower the wyrmling for one day. I'd equate it to summoning a CR1 monster similar to the various summoning spells.

So, firstly I'd have limited the size of the pet. It can only be small or tiny. Nothing more than that. Likewise, I'd have limited to beasts most likely. 

However, if they are stuck on a dragon or dragonkind, I would scale down and give the creature the Pseudodragon stat block. That thing is far more appropriate for a pet than a Wyrmling. 

What I would suggest here though is that this is a problem of being very permissive with players while not considering the ramifications of such an approach. Sometimes limits are needed. Which is why I would suggest limiting pets by size. Limiting by to either Small or Tiny and limiting to say Beast, Construct, Dragon, Elemental and Plant creature types I don't think that there is a potential pet there that is higher than a CR of 2. That to my mind keeps the pets limited to a reasonable level, and allows a great deal of choice. I'd imagine with those constraints there would still be like 100-200 options for a pet available.

Edit - as an additional point. If you are going to allow players to have pets and if they are going to be allowed to engage in combat, then you have also effective neutralised the themes and special features of several classes. Beast Master Ranger is a great example of this. The entire point of that class is now gone if you give your players pets as standard. So, I would strongly advise disallowing that subclass as an option for players. This way players aren't going to feel hard done by if they chose that class but everyone else has effectively the same things that make them special (assuming just PHB, MM, and DMG).

Quote from Greenstone_Walker >>

GM: You have a pet stunted dragon. Now, pets are noncombat features. During a combat it will be assumed to be either hiding or having its own combat just off-camera and not controbuting to the main combat. If you want your pet to take part in the main combat then you need to make your character a summoner of some kind, or a beast master ranger, or something like that. No, I'm not giving you a combat pet for free - that wouldn't be fair to the people who are playing summoners and who have to spend resources to get their combat allies.

 This this this.

If you want a pet for roleplay purposes, that's fine. If you want a huge combat benefit that no one else gets, that's gonna be a no from me dawg.

Quote from Thorn_of_Eld2 >>

Hey, I'm pretty new to Dming and i have a slight dilemma. Our friend group has always had it so druids get pets/familiars. idk we all just wanted that. Now one of my players wants a stunted copper dragon wyrmling as hers. How do i make that balanced? Health wise, we always just do that your pet's health is half of yours, rounded down. But that thing is still too much. 

 If you are new to DM'ing, you are entering into a world of hurt when giving PC's "pets" like the ones that have been described. The best thing a new DM can learn is the word "no" and the courage to stick by using that word.