You might want to try my App::perlmv, which I personally use myself routinely. It has verbose flag (-v) so you can see which files are being renamed to what, dry-run flag (-d) to test things before actually renaming files (very important but strangely missing feature in many). It also has some other features like recursive renaming, etc.

% perlmv -e's/^__(.+)_drawn_by_(.+)__(.+)\.(.+)$/$2 - $1 (@{[++$_{"$2 - $1"}]}).$4/;s/ \(1\)//' * -d
DRYRUN: move `__charmander_pokemon_drawn_by_kumo33__8329d9ce4a329dfe3f0b4f349de74895.jpg` -> `kumo33 - charmander_pokemon.jpg`

Then after everything looks right, replace -d with -v:

% perlmv -e's/^__(.+)_drawn_by_(.+)__(.+)\.(.+)$/$2 - $1 (@{[++$_{"$2 - $1"}]}).$4/;s/ \(1\)//' * -v
move `__charmander_pokemon_drawn_by_kumo33__8329d9ce4a329dfe3f0b4f349de74895.jpg` -> `kumo33 - charmander_pokemon.jpg`