So ... like I said, Pikachu is not a favorite of mine and made a derpy one at the bottom but since there rest is more defiened ... I felt I needed to add a similar style to that critter.  

From the top and downwards.

Pachirisu
Electric type but looks like an ice type from it's coloration but that is only because of the area it lives in. Colder areas like tundra and similar. It got thick fur and denser around the spine that slowly evolved into scales like material. Even the tail have 3 spikes which it use as defense.

Pichu
Kit version of Pikachu.
Wider ear base and even fluff sticking out to make them look bigger and black fur around their neck which can be seen as strips or spotted lines down along their back for camouflage. Defense mechanic is to hide or run to shelters by older pikachus. It is to small to store enough or handle electric moves other than light shocks which have saved some of the kits when grabbed by trainers or predatores.

Marill
(I know Marill line is not electric type but it was based on pikachu in looks so it stays there).
Being the water version and fairy, it lacks the eletric sacks on it's cheeks but being an earlier branch of the family that holds Pikachu as one of the later branches. It still have the basic shape. Short forelimbs, bean shaped body, longer backlegs and long tail. Ears are counted as well even tho they are bent down in this stage (few individuals have straight ear the whole time) but they can be opened up when needed to listen more closely. As the bent ears gives better protection while in water and the fur is bit more denser as well but short along the skin and lets water drip off quicker because of the slightly oily texture. 
Webbing on all four paws give it better movement in water.

Emolga
The flying squirrel version and second smallest in the family.
True to the look of one with it's fluffy tail that will help it move around in the air. Generally it will need height to jump off from to fly but it got a trick thanks to it's electric nature that it can generate static air underneth it's wing to give push to stay in air longer or jump from if needed. 

Dedeene
Smallest in the family.
They are know to be steal sweet food if given opportunity and given their small stature they can easily hide where other pokemon and trainers cant reach them. Even small ones can pack a good punch with their electric attacks and nuzzling any in the family can make a person paralyzed for a short time. 
Being a fairy type as well, it have ways of charming others to let it closer but doesnt seem that interested in other moves but can be trained. For being a small critter it does move very fast when needed.  

Azumarill
Adult stage and guardian.
Better diver and stays in water for long periods of time but can be often seen wandering around shores and rivers to keep of other pokemons that would be a threat to it's clan. Ears are fully erect in this stage and the short fur from marill have gotten denser and slightly longer on Azumarill, especially around the neck and the front of it's body.
They are known to use their claws on both forelimbs and backlegs to deal damage against other pokemon but they seem to have a rule to avoid damage in the clan, as they attempt to wrestle down the opponent instead to see who is stronger to defend or lead.

Pikachu
The electric mouse, known for it's shocking abilites and stubborn attitude.