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.
0600Patch 6.1.0 (24-Feb-2015): Chimaera Shot damage increased by 30.4%.
0600Patch 6.0.2 (14-October-2014): Chimera Shot has been renamed Chimaera Shot. It is now a two-headed shot that hits two targets, costs 35 Focus (down from 45 Focus), and deals Frost or Nature damage, but no longer heals the Hunter.
0500Patch 5.2.0 (5-Mar-2013): Chimera Shot now deals 25% more damage and heals the Hunter for 5% (was 3%) of their total health.
0400Patch 4.0.6 (8-Feb-2011): Chimera Shot’s overall damage has been increased by roughly 50%.; Chimera Shot’s particle effect animations should now display correctly.
0300Patch 3.1.0 (14-Apr-2009): Mana cost reduced from 16% to 12%.
0300Patch 3.0.8 (2009-01-20): The secondary effects of this shot will now still be triggered even when the target dies from the ability's damage.