Cool idea, Phoenix! Count me in!
Let's see...
Name: Banshenon
Type: Ghost
Species: Leech
Height: 2'3"
Weight: 38 lbs.
Element: Xenon
Evolution: None
Image: A glowing blue-yellow ball of gas with a 'scary face (kinda like Gastly's)' and rings of plasma running around it three ways (like that thing that astronauts train in).
Pokedex Entry: Commonly found floating around neon signs at night, it saps electrical energy from the signs, often resulting in mild power outages. Though normally a fearless Ghost-type, it is not at all fond of water...
Name: Mermes
Type: Water
Species: Myth
Height: 1'2"
Weight: 24 lbs.
Element: Mercury
Evolution: Basic
Image: A sky-blue fish with stubby forearms, green ridges on its midsection, and seaweed-like hair. Quite feminine-looking.
Pokedex Entry: Created when a myriad of aquatic DNA was genetically force-fused with mercury. It is believed to contain trace amounts of unstable human DNA...
Name: Hypatherm
Type: Water
Species: Liquid
Height: 2'6"
Weight: 65 lbs.
Element: Mercury
Evolution: Evolves from Mermes at Level 16
Image: An icy-blue fish with human forearms, long seaweed hair, and sharklike fins on the back. Still feminine-looking, but much more fierce.
Pokedex Entry: The mercury in its blood makes its body highly unstable. Can melt into a currently unidentified substance when alarmed.
Name: Thermaid
Type: Water/Steel
Species: Oceanic
Height: 5'8"
Weight: 145 lbs.
Element: Mercury
Evolution: Evolves from Hypatherm at Level 32
Image: A silver fish with an amazingly human-looking upper body, clam-shaped patterns over its chest and shoulders, and kelp-like hair. Looks almost like a true mermaid, but... not quite.
Pokedex Entry: Maximum evolution has synchronized its mind and body, perfecting its liquifying powers. Prefers to be in its liquid form more than in its solid form.
I'm too tired to think of any others, but when I come back, I'll have some more.
-Blade
EDIT: Mermes was meant to be the Water starter, by the way, but if it doesn't make the cut...
Oh, well...
EDIT 2: I personally liked the name 'Lithger' better, if that helps or matters.