you spit a bit of ink in the face of an enemy up to 15 ft away. he has to make a dex save against a DC of 10+ 1/2 your character level or is blinded until he splashes water in his eyes (its not washed away automatically under water but the saves are done with advantage) or  suceeds the dex save he can repeat at the end of his turn. you gain charges equal to either your dex or strenght modifier×2 (choose once at character creation) and can spent one to use ink splat. all charges are restored once you do a long rest.

at 5th level you can use 3 charges to spit ink in an 10 ft cone

your swimming speed is equal to your walking speed and you dont have any the disadvantages of being underwater. you can breathe freely underwater and gain 120ft of darkvision underwater.

dex+2 any other skill+1

Sud'har, walking on land are mostly medium sized ranging from 5-7 foot your size is medium

the sud'har get very old, up to 1000 years, but can only walk on land at the age of 60-140 before their humanoid libs start to get more like tentacles

Climbing speed 10 and you can do unarmed attacks with them for 1d4+strenth modifier bludgeoning or use small weapons like daggers or handaxes to make one extra attack with disadvantage as a free action once a turn 

at level 5 two extra tentacles sprout and give you a climbing speed of 20 as well an the option to either do an attack with one tentacle or your normal arms