Peng You Lightfoot was an advanced lightfoot Vagabond skill which was probably implemented on patch 98, 99 or 100 through [Tome] Antidote of Cave newly appearing in-game as a drop. The skill remained in-game until it was changed on patch 125 to a non-functional skill, and later on to Poison Resistance in the Cave of the Conqueror.
Peng You Lightfoot was originally a skill one could receive as reward through Acclaim's "friends invite" program. Through Acclaim's Website, one could invite a friend, and if that person would register and join the game, the inviter would receive the Peng You Lightfoot skill, supposedly on C12, for 24 hours.
After GamersFirst took over the 9Dragons publishing contract in 2010, they also pretty much took over the current state of the game. Shortly after they took over, the skill from [Tome] Antidote of Cave changed to a non-functional skill. G1, or more precisely G1's 9Dragons Community Manager, promissed the players to let the developer Indy21 implement the advanced vagabond lightfoot back into the game. The official statement was that the vagabond lightfoot would be re-implemented, and about 10% faster. However, the non-functional skill was then replaced with the vagabond skill Poison Resistance in the Cave of the Conqueror, and with the implementation of the Bamboo Village beginners map, Indy21 also implemented the basic vagabond lightfoot Cruising Along (which is just as fast as any other basic clan lightfoot), and considered this to be the re-implementation of the vagabond lightfoot players asked for.
It is questionable whether this was a mistake and/or misunderstanding from Indy21. It is also uncertain whether GamersFirst did not have the interest to keep bothering Indy21 about the real advanced vagabond lightfoot, or if Indy21 simply refused to do so and/or ignored GamersFirst's request.
To this day, even though Indy21 closed and different developers took 9Dragons over, there has never again been any sort of advanced vagabond lightfoot implemented in-game again.
Peng You Lightfoot's animations and effects were the very same as the advanced Heavenly Demon lightfoot.
"Peng You", or "péngyou" (朋友), means "Friend" in Chinese.