Chimera Shot is a hunter ability learned at level 60 for hunters who have chosen the Marksmanship specialization. It is an instant shot that causes damage, refreshes [Serpent Sting], and heals the hunter for a small amount. There is no limit to the number of times that Serpent Sting can be refreshed, meaning that it stay up indefinitely by using Chimera Shot. When used with Serpent Sting, Chimera Shot is one of the Marksmanship hunter's highest damage abilities on a single target.
With Chimera Shot, a Marksmanship hunter has three high-damage instant cast shots on different cooldowns ([Aimed Shot] (with [Master Marksman]), [Arcane Shot], and Chimera Shot), and four if you include [Kill Shot], which only works when the enemy is below 20% health. With all these instant shots, a hunter can deal a decent amount of burst damage without ever standing still. This gives Marksman hunters an edge in PvP where they generally do not have the opportunity to stand still for long periods of time.