Blobfish feature where they get disadvantage on CHA when outside of water due to lower pressure
Trait for riding aquatic creatures
no disadvantage for ranged attacks underwater
Draconic cry doubles range underwater
Kobold (Deep)
Deep Swimmer. You have a swimming speed equal to your walking speed, and you can breathe underwater.
Glowstalk. You have a bioluminescent stalk extending from your head. As bonus action, you can let out a pulse of dim light out to 20 feet until the start of your next turn. You and your allies have advantage on attack rolls against enemies within this dim light who are not also within bright light. If any of these attacks hits a creature that has an Intelligence score of 4 or lower, the attack deals an additional 1d6 damage.
You can use this trait a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.
This may need a bit more tweaking but I'm likeing the concept
Deep Legacy. Adaptations to thalassic depths can manifest is different ways for each kobold. Choose one of the following legacy options for your kobold.
Aquatic Cavalier. You can mount or dismount a creature that has a swimming speed with only 5 feet of movement.
Extreme Depths. Acclimated to low temperatures and high pressures, you have resistance to cold and thunder damage.
Thalassic Sniper. Being underwater does not cause your ranged weapon attacks to fail at long range, nor does it impose disadvantage at normal range.
Fluff
Just as dragons can be found in every corner of the material plane, so too can kobolds. This includes the deepest reaches of the ocean, where sunlight is as alien as extraplanar beings. WIP
In Alvergia, deep kobolds are very rare, and typically only found at the very bottom of the deepest oceans. Very few make it to the shallower seas, even fewer to the surface. However, small groups have been known to mingle with other groups of aquatic peoples, particularly around the lonely islands. Deep kobolds have occasionally been spotted seemingly riding whales and tohorans in the depths of the Azure ocean. The relationship exhibited here is unclear.
Discarded, undecided
Glowstalk You have a bioluminescent stalk extending from your head. As a bonus action, you can start or stop the stalk glowing, emitting dim light out to 15 feet. While the stalk is glowing and you are not in bright light, you have advantage on attack rolls against each creature within 15 feet that has an Intelligence score of 4 or less.
Something like this could replace draconic cry, giving allies advantage
Aquatic Cry. As a bonus action, you let out a cry at your enemies within 10 feet of you, or within 20 feet of you underwater. Until the start of your next turn, you and your allies have advantage on attack rolls against any of those enemies who could hear you. You can use this trait a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.
jackhaydock
commented
1 year ago 
Deep ocean kobold
Ideas:
Kobold (Deep)
Deep Swimmer. You have a swimming speed equal to your walking speed, and you can breathe underwater.
Glowstalk. You have a bioluminescent stalk extending from your head. As bonus action, you can let out a pulse of dim light out to 20 feet until the start of your next turn. You and your allies have advantage on attack rolls against enemies within this dim light who are not also within bright light. If any of these attacks hits a creature that has an Intelligence score of 4 or lower, the attack deals an additional 1d6 damage. You can use this trait a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.
This may need a bit more tweaking but I'm likeing the conceptDeep Legacy. Adaptations to thalassic depths can manifest is different ways for each kobold. Choose one of the following legacy options for your kobold.
Fluff
Just as dragons can be found in every corner of the material plane, so too can kobolds. This includes the deepest reaches of the ocean, where sunlight is as alien as extraplanar beings.
WIPIn Alvergia, deep kobolds are very rare, and typically only found at the very bottom of the deepest oceans. Very few make it to the shallower seas, even fewer to the surface. However, small groups have been known to mingle with other groups of aquatic peoples, particularly around the lonely islands. Deep kobolds have occasionally been spotted seemingly riding whales and tohorans in the depths of the Azure ocean. The relationship exhibited here is unclear.
Discarded, undecided
Glowstalk You have a bioluminescent stalk extending from your head. As a bonus action, you can start or stop the stalk glowing, emitting dim light out to 15 feet. While the stalk is glowing and you are not in bright light, you have advantage on attack rolls against each creature within 15 feet that has an Intelligence score of 4 or less.
Something like this could replace draconic cry, giving allies advantageAquatic Cry. As a bonus action, you let out a cry at your enemies within 10 feet of you, or within 20 feet of you underwater. Until the start of your next turn, you and your allies have advantage on attack rolls against any of those enemies who could hear you. You can use this trait a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.