Slither the Snake was bag number 2 in the Pet Pals group of the 2000 McDonald's Teenie Beanie Babies promotion. That year's Happy Meal phase used 18 numbered bags across five categories running from June to November 2000, the biggest of the four U.S. Teenie promotions, with several more special groups sold outside the numbered sequence. Slither carries McDonald's branded swing and tush tags rather than Ty's heart tags, and like most of the promotion, it was made in huge numbers, so a sealed bag alone is not a value driver.
The full-size Slither the Snake has its own record here.