Good evening!

I'm a DM and am hosting a variety of characters. For one of them, I just can't seem to get down for a subclass. They are playing as a monk, and I have helped them create a race, but I cannot figure out how their subclass should go. They want something to do with electricity, as their race involves that. Their race is a dragonborn that is the descendent of an electric-eel dragon. So figuring out a fluid- yet electrifying monk subclass has been difficult. I've made many homebrew things before, but they have almost all been Races, as my friend is often the one to make classes and subclasses. I am looking for advice on how to properly make this subclass, without going to AI for answers.

One thing I was thinking was to utilize the slick nature of their race. As an (basically) eel descendent- they produce a natural, slime-like substance that allows them to slip through a space one size smaller than them, as well as making enemies have disadvantage on grapple checks. Are there ways I can use this in a subclass for monks. The player uses a quarterstaff as a weapon. We are currently using 2014 5e.

(Any feedback would be appreciated! Thanks for reading!)

Edit: I just finished a rough draft of the subclass, it is called 'Way of the Abyssal Spark'.

Level 3: Depth’s Grasp

The deepest parts of the ocean, the abyssal zone, has become a part of you. You can feel the way that electricity flows through the air, allowing you to alter its flow. Whenever you grapple, or are grappled, you can spend 2 ki points to use a reaction that releases a wave of lightning into the other creature. The damage is equal to your martial die + Wis modifier, dealing either lightning or thunder damage (chosen on use). The creature must roll a constitution check- with a dc of 12, or else be paralyzed for one turn. At level 6 the DC changes to 14, level 11 DC 15, and at level 17, the DC becomes 18.

Level 6: Electric Slide

At 6th level, you gain the ability to slide through the battlefield. You gain the cantrip Electric Slide. You can produce a slime-like substance under you, and flow your lightning through it. This allows you to slide over any terrestrial or aquatic terrain for 15ft. This does not spark a reaction if you slide by an enemy. This counts as your attack action. At level 6 it’s 20ft, level 11 is 25ft, and level 17 is 30ft.

Level 11: Paralyzing Wave

Using three ki points, you can launch a paralyzing wave of thunder around you, in a 10ft radius- if in water, the range is 15ft.. Any creature in that radius has to roll a constitution saving throw, DC 15, or take 2d6 thunder damage, and be paralyzed for two turns. On a success, the creature takes half damage and is not paralyzed. At level 17, the DC becomes 18 and does 2d8 instead.

Level 17: Abyssal Threat

Immunity: You gain immunity to Lightning and Thunder damage.
Abyssal Sight: In water, you gain the effects of Blindsight.

Oceanic Threat: Using 5 ki points, you condense the water in the air and launch an explosive web of water and lightning in a 30ft radius around you. It does 4d8 lightning damage, and forces all creatures in the range to make a constitution saving throw with a DC of 19. On a fail, they are paralyzed for 3 turns. On a success, they take half damage and are paralyzed for one turn.

Are there any ways that I can improve/balance this better? Again, this is my first ever attempt at making a monk subclass. Any advice would be appreciated!