Bullseye: Perfect Game

A two issue book

'Bullseye accepts a contract to kill a professional baseball player'

http://www.comicbookresources.com/?page=article&id=28342

This book has his most impressive kill to date. Somehow sneaking onto Genosha, putzing in within a few hundred meters of Magneto without being noticed despite the extra pounds of adamantium he's slinging around, and then killing a mutant with indestructable skin a few feet away from Magneto with a metal, poisoned needle to the ear.