but It won't have the stats and the level. say ditto was level one and he/she fought a mewtwo and used transform
you would still be screwed.
mew and mewtwo can turn into any pokemon also.

Theoretically.

Refer to "Asycaths Theorem Of Steelix"

Fig 1. Trainer innocently walking dawn route.
Fig 2. Ditto Jumps out
Fig 3. Ditto transforms into Steelix
Fig 4. Trainer screwed.

MEW2

lvl 1 ratata
moves-
•quick attack
•endure
•endeavor
•(anything else)
item- focus sash
how to use- use endeavor. the opponent should strike an attack first, and the focus sash allowing 1hp. endeavor allows an attack that leavs the same amount of hp you have. now use quick attack which always goes first.

there is no most powerful pokemon, it just depends on move sets. and defense.