How about base stats that add up to a certain number (say forty) and each creature has them in different amounts in different places in their stats...?
Awful Example(It doesn't have to be those exact ones~ XD):
Wyndragon-
Attack: 5
Defence: 6
Health: 10
Speed: 11
Precision: 7
There wouldn't be any bonuses in RP areas, but there could be something of a shop where you can get 'upgrades' to your creature. But it would work in percentage? Say the lowest a base stat would be is 5(or something, XD) , everything in the shop would give you + %20 atleast, if my maths is right, lawl. XD I'd be happy to draw the items~ XD We could give them stupid names, like:
The Saucepan of Justice! (This saucepan with increase your pet's defence by + %20
The Pretty Pink Potion of Precision!
The owners of the creatures could decide the stats, like the person that made the pet. Then we could keep them in a topic somewhere all nice and neat. Customs randoms could have one set of stats, while premades and 'official species' have others, but that's upto the creator of that creature.
As for actual battling, I've got no clue. XD But that's my idea for the actual stats, something that doesn't confuse people like me silly and would mean that the creators of the creatures could decide stats easily themselves.
Also, my scriblin is adorable <3 -luffs eet-