, take a Charmander and name it Scorchie.
This little lizard isn't really aware that it's a fire-type.
As such, it can never use STAB moves.
It can evolve after it soloes every trainer in a gym except the gym leader on the first try.
If it evolves to Charmeleon, Scorchie begins to wonder about typing.
If it gets hit with three fire-type moves, it realizes it's a fire-type and can use STAB moves from now on.
However, since it is still getting used to it's new-found abilities, it can only use them when Blaze has activated.
It can evolve again after KOing 5 trainer-owned Pokémon with fire-type moves.
If it evolves to Charizard, it becomes a totally aggressive pyromaniac.
All previous restrictions no longer apply, but it can only use fire-type moves.
It can never be switched out manually, only after it is KOed, because it goes berserk every time it's in battle.
It also cannot carry held items, as they would be burnt to a crisp.
It must solo Lorelei, no matter how many times it has evolved.
EDIT: Now that I have some more time, I'd love to throw my
Chikorita into the ring.
, take a Chikorita and name it Petal.
This Chikorita is highly impressionable, so it is very involved with the type of the first Pokémon used against it during each battle.
In the case of dual-typed Pokémon, flip a coin to decide. Heads=type#1, tails=type#2.
Ignore the above restrictions until level 9. Good luck!