In Alan Wake, you fight inanimate objects that have been taken over by the Dark Presence.
These are called Poltergeists or Poltergeist Objects. Most of them attack by flinging themselves at Alan.
But Poltergeists like earth-mowers and tractors usually try to mow Alan down.
The possessed Objects frequently appear throughout the game. At the beginning, the only Poltergeists appear as locked gates blocking the way for the player. They don't start directly attacking Alan until Episode 3: Ransom, where a number of pipes comes to life beneath a bridge.
The most common Objects are oil drums, car tires, and similar. These can often be "killed" by the time they are ready to attack the first time.
In some situations, you might come across huge cement pipes, or pieces of a train-wreckage. These will require more time to take down.
In several situations Alan might come across some sort of boss, these are more often than not a rather large vehicle.
The first one, a bulldozer, appears in Episode 3 after leaving the bridge.
The second in Episode 4: The Truth, this is a combine harvester found in The Anderson Farm. Also, there is a tractor, but it is considered more of a mini-boss as it cannot do too much in the way of attacking and can be taken out rather easily.
In Episode 6: Departure, on the first bridge, small crane comes to life, but is considered more of a mini-boss, as even though it attacks in various ways and is harder to kill than a regular big object, it can be taken down with two flares. A monster truck attacks Alan after leaving the bridge, but it's not necessary to defeat it. The Dark Presence throws a school bus at Alan, but it's easy to avoid it. Finally, a bulldozer will appear when Alan is making his way through a scrap-yard.
In Special 1: The Signal, the Deerfest parade truck reappears, but this time, it's thrown at Alan. Later, taken monster trucks appear as optional mini-bosses in a certain section, and the final boss of the special is a large conglomerate of televisions.