This viridian cape is shot with threads of greenish metal.

A cape of the viper allows you to transform into a poisonous serpent. The cape has 3 charges, which are renewed each day at dawn. Spending 1 or more charges transforms you into a viper for 7 rounds.
1 charge: Small viper.
2 charges: Medium viper.
3 charges: Large viper; add +2 to the save DC of your bite’s poison.
While in viper form, you replace all your normal statistics and special abilities with those of a typical viper of the appropriate size, except for your alignment, your hit points, your Hit Dice (for the purpose of adjudicating effects based on HD), and your ability to understand (but not speak) the languages you normally understand.
Any gear worn or carried melds into the new form and becomes nonfunctional. Treat this as a polymorph effect, as defined on page 95 of Player’s Handbook II.

Prerequisites: Craft Wondrous Item, ability to wild shape.
Cost to Create: 1,000 gp, 80 XP, 2 days.