So, I am the DM of a campaign that is completely from scratch, and I'm basically just taking the bits and pieces that I like from the official campaign supplements that are out there. My campaign features merfolk prominently, and since merfolk aren't an official race, I made one. I would like some feedback on it, as it is my first time and I have lots of room to improve. Click on this link to see the details page. If, for whatever reason, can't pull the page up, tell me and I will try to fix it.

 Well you didn't give them an age, size, or movement speed.

There are already sea dwelling races the sea elf and the triton that you can look at for inspiration.

As far as what you have goes, I think it's a good start. The dexterity boost makes sense because of the merfolk's ability to orient themselves in the water, although I'd like a little more explanation for the Intelligence boost. Is it because they're descended from an advanced ancient civilization, or because they're curious? Additionally, I think that Amphibious feature is okay, but not particularly useful if the mermaids have no way to move across land. Surfacing to talk to humans is understandable, but I think that feature needs a little more umph. Also, when you add movement speed, be sure to specify a swim speed, since that's technically different according to 5e rules.

 I would definitely take DxJxC's advice and check out the sea elf and triton races for inspiration, but again, a good start! And lots of excellent flavor text.

You can also check out the merfolk from plane shift: ixalan and zendikar. They're not as good as the official 5e races (imo), but a larger sample size never hurts.

Quote from JankShenanigans >>

As far as what you have goes, I think it's a good start. The dexterity boost makes sense because of the merfolk's ability to orient themselves in the water, although I'd like a little more explanation for the Intelligence boost. Is it because they're descended from an advanced ancient civilization, or because they're curious? Additionally, I think that Amphibious feature is okay, but not particularly useful if the mermaids have no way to move across land. Surfacing to talk to humans is understandable, but I think that feature needs a little more umph. Also, when you add movement speed, be sure to specify a swim speed, since that's technically different according to 5e rules.

 

 
The Intelligence boost was because they are curious, I will definitely specify on that, and I gave them a swimming speed and walking speed, but it must not have gone through. I will edit that, as well as their size(Medium) I mentioned the age briefly, but I'll write it again. I will definitely check out the plane shift content, and thanks to all of you!

I've added their size, age,  speed, and my reason for the Intelligence boost

Also, in case anyone is wondering, these merfolk are based (more or less) on the ones in the Monster Manual.

 It seems very lacking in features.

Standard ability score increases, water-breathing, and a single weapon proficiency? It has even less than the Dragonborn.

 most classes have simple weapon proficiency's so change it to trident  

according to page 218 of the monster manual, intelligence aint one of their racial traits, dex con and charisma are the 3 which get a boost in there for the average merfolk, so you might want to reconsider that. 

in my own personal world i considered their use of only spear a bit boring so i've changed mine to trident and net for a bit of extra flavour.
i also gave them a special material for making their nets which is strong a lightweight and isn't impeded when thrown through water. but it has to be kept wet or it goes brittle 

Hey cryomancer!

After reading some of the other posts in this thread, one option to flesh out the abilities of the merfolk may be to give them some inherent spellcasting ability, like Drow Magic. I think this would work well for your race because their history is tied to their leader's ancient patron deity. Create/Destroy Water, Elemental Weapon, Water Walk, Armor of Agathys, Shape Water, Tidal Wave, and Wall of Water could all be potential spells to use for this ability. (I wouldn't suggest using all of those spells though XD)

Watery Sphere is another good one.

Quote from JankShenanigans >>

Hey cryomancer!

After reading some of the other posts in this thread, one option to flesh out the abilities of the merfolk may be to give them some inherent spellcasting ability, like Drow Magic. I think this would work well for your race because their history is tied to their leader's ancient patron deity. Create/Destroy Water, Elemental Weapon, Water Walk, Armor of Agathys, Shape Water, Tidal Wave, and Wall of Water could all be potential spells to use for this ability. (I wouldn't suggest using all of those spells though XD)

 I like this idea and would like to add waterbreathing as a ritual to the options so they can invite non-aquatic races as guests.

Quote from DxJxC >>

Quote from JankShenanigans >>

Hey cryomancer!

After reading some of the other posts in this thread, one option to flesh out the abilities of the merfolk may be to give them some inherent spellcasting ability, like Drow Magic. I think this would work well for your race because their history is tied to their leader's ancient patron deity. Create/Destroy Water, Elemental Weapon, Water Walk, Armor of Agathys, Shape Water, Tidal Wave, and Wall of Water could all be potential spells to use for this ability. (I wouldn't suggest using all of those spells though XD)

 I like this idea and would like to add waterbreathing as a ritual to the options so they can invite non-aquatic races as guests.

 Thank you! I will do that. And I will also change the proficiency to a trident. I did spear because honestly, they are the same thing as tridents, but it is true that most classes already get simple weapons, so I will make that fix.

Once again, thanks for all the help you're giving, and I will make the fixes as soon as I can.

Quote from Captaincarrot1889 >>

according to page 218 of the monster manual, intelligence aint one of their racial traits, dex con and charisma are the 3 which get a boost in there for the average merfolk, so you might want to reconsider that. 

in my own personal world i considered their use of only spear a bit boring so i've changed mine to trident and net for a bit of extra flavour.
i also gave them a special material for making their nets which is strong a lightweight and isn't impeded when thrown through water. but it has to be kept wet or it goes brittle 

 I looked at the monster manual, but I overlooked that part. Thanks for bringing it to my attention, I will probably change it. Also, the idea for the material of their nets is great. I'll be sure to slip it in. I'm trying to do the character sheets digitally, so is your net in the homebrew equipment section on D&D Beyond?

I'm going to update the innate spellcasting part just as soon as I can buy armor of agathys in the marketplace. All the other stuff is going to be updated shortly

Trident & Net proficiencies and Ability Score increases have been changed. About to do the water breathing as ritual

Quote from mastercryomancer >>

I'm going to update the innate spellcasting part just as soon as I can buy armor of agathys in the marketplace. All the other stuff is going to be updated shortly

 Just remember you can't publish a homebrew that has spells, feats, items, etc. from a book other than basic rules (srd).

Quote from mastercryomancer >>

Trident & Net proficiencies and Ability Score increases have been changed. About to do the water breathing as ritual

 Honestly, you can probably keep spear proficiency and add trident, net, and even javelin (just to cover bases). Elf weapon trainings include 3 or 4 weapons including martial and simple.

You can also give the shape water cantrip.

Quote from DxJxC >>

Quote from mastercryomancer >>

I'm going to update the innate spellcasting part just as soon as I can buy armor of agathys in the marketplace. All the other stuff is going to be updated shortly

 Just remember you can't publish a homebrew that has spells, feats, items, etc. from a book other than basic rules (srd).

 

Quote from mastercryomancer >>

Trident & Net proficiencies and Ability Score increases have been changed. About to do the water breathing as ritual

 Honestly, you can probably keep spear proficiency and add trident, net, and even javelin (just to cover bases). Elf weapon trainings include 3 or 4 weapons including martial and simple.

You can also give the shape water cantrip.

 I was planning on armor of agathys, but I didn't realize that you couldn't publish stuff that doesn't have the basic rules options, so I'll just tell you what their Innate Spellcasting looks like. Also, thanks for your suggestion, I will add javelin proficiencies, probably won't keep spear, because as other people have mentioned, it is just the same thing as trident and a lot less flavorful. (Although it is less gold)

 Here's their Elemental Magic feature.

Their patron, Halkana, granted them part of his elemental power as part of their deal with him.

You know the shape water cantrip. When you reach 3rd level, you can cast the create or destroy water spell as a 2nd level spell once with this trait and regain the ability to do so when you finish a long rest. When you reach 5th level, you can cast the armor of agathys spell as a 2nd level spell once with this trait and regain the ability to do so when you finish a long rest. Intelligence is your spellcasting ability for these spells.