Try this out. . .
function cwc_pkmn( $atts = array(), $content="" )
{
// ------------------------
// Settings:
$path="https://wordpress.stackexchange.com/path/to/file/";
$ext="png";
// ------------------------
// Shortcode input:
$atts = shortcode_atts(
array( 'name' => '' ),
$atts,
'pkmn_shortcode'
);
// Sanitize input:
$name = esc_attr( $atts['name'] );
// Init:
$words_ucfirst = array();
// Capitalize the first letter in each word:
$words = explode( '-', $name );
foreach( $words as $word )
{
$words_ucfirst[] = ucfirst( $word );
}
$name_mod = esc_attr( join( ' ', $words_ucfirst ) );
return sprintf( '<img src="https://wordpress.stackexchange.com/questions/151323/%s%s.%s" alt="%s" title="%s" />',
$path,
$name,
$ext,
$name_mod,
$name_mod
);
}
add_shortcode( 'pkmn', 'cwc_pkmn' );