After the 당신 defeat your shadow, 당신 face the 'Mysterious Warrior'. After the 당신 defeat him, he gives his dying speech and 당신 later find Marian returned to life. The Nes & PC Engine version feature this ending.
The first Double Dragon game, please note that i'm not going to post the nes version here becuase it was infamous for lacking co-op play, making Jimmy a boss & an awful vs. mode