Huorn

Huorns are passive (until angered) mobs that spawn in Fangorn Forest. They appear as regular oak, birch, or beech trees until attacked or disturbed, then angry faces appear on them and they come to life.

There are two variants, the regular Huorn and the Dark Huorn (see section below). Both have 60 health.

Upon death, a Huorn or Dark Huorn will drop logs of their tree type and/or sticks.

Combat
Huorns are as fast as a sprinting player, and are not hurt very much by swords. Fire and axes are the best way to defend yourself, as axes will do much higher damage than swords to this enemy. Poison can also hurt them.

Killing a Huorn will lower your Fangorn alignment, however. It earns you the achievement "Lumberjack".

Dark Huorns
Dark Huorns spawn in the Old Forest and are hostile to all players. They will attack you if you try to cut down a tree in the Old Forest, regardless of one's alignment. They may also attack if you get too close to them.

Like the regular Huorn, it is best to combat this foe with fire or axes.

Killing a Dark Huorn will give you the achievement "Forester's Nightmare".

Hiring Huorns
As of Beta 19, hired Huorns can be created. For that you need golden Ent draught and at least +500 Fangorn alignment. Just take the golden Ent draught in one hand and right-click a sapling (oak, birch or beech). Make sure there is enough space above the sapling to actually spawn the Huorn.

When a Huorn is hired, it has much of the same mechanics as other hire-able units. They can be set to guard mode or dismissed, and a green bar above their head shows their health. They do, however, have a special method of being summoned. All the player needs to do is to drink the golden Ent draught.

Note that evil players can't hire Huorns or Dark Huorns.

Be warned: If you hire a Huorn and chop a log block of any tree in any biome (even outside of the Fangorn Forest) the Huorn will desert you (abandon you as a hired unit). And if that's not bad enough, it will also start to attack you immediately. Even then, killing it could lower a lot of alignment with Fangorn.

Trivia

 * Huorns are guarded and looked after by the Ents that spawn in Fangorn Forest.
 * They are the strongest units that a good player can hire; their immunity to all weapons save axes and their great speed make them great bodyguards. Their cost and alignment that is needed to hire them balance this mob out though.