A new generation of pokémon

[TomGuycott]

Also if you wanted to consider the kind of themes that the actual games use, these are observations people have made about the starters over the generations of pokemon:

The Grass type has always seemed to be some kind of reptile.
The Fire type has been animals from the Chinese Zodiac
The Water type has been aquatic animals (easy).

However I feel like making a theme is the least of your worries. Practice your sprites for a while.

... for some reason I like the fact that they blink, though. xD