The skill releases a spear-like projectile that encumbers the target with ethereal chains and also does a percentage of weapon damage. If the target is close to other enemies, they will also be linked into the chain and slowed.
The following is a very quick summary. See the Entangling Shot rune effects page for a more thorough description of rune effects, or any of the individual rune pages for numbers, screenshots, blue quotes, and much more.
Entangling Shot largely works as a debuff; the target is greatly slowed by chains that hinder movement. Any monsters near the target are caught in the chains and slowed as well. This skill also does a small amount of damage to the target; however, the damage is small enough that the skill's main utility is for crowd control.
It’s largely a debuff; each shot ensnares enemies with a black chain that glows purple, and greatly slows their movement for several seconds. The arrow can hop between multiple targets, chaining them together for the duration. The damage dealt by the arrows is negligible though, so this was almost purely a defensive skill.
Skill tiers were removed shortly before the beta started in September 2011, and Entangling Shot became a level 2 skill, but was soon changed to level 8. The skill system was once again overhauled for the Beta Patch 13, and Entangling Shot was classified as a Primary skill and moved up to level 11. For Beta Patch 14, it was dropped to level 3.