You won't be able to simply walk up to the Haunted Carriage

What you need to know about the Haunted Carraige event in Diablo Immortal can be found here Diablo 4 Gold.

You won't be able to simply walk up to the Haunted Carriage whenever the mood strikes you, as is the case with many of the zone events in Diablo Immortal. In point of fact, the opportunity to participate in that event is extremely limited.

At Ashworld Manor, the Haunted Carriage spawns every Tuesday and Saturday at 12 p.m., 8 o'clock at night and 10 p.m. (based on your local server time). To avoid missing your shot, it is generally recommended that you arrive at the manor at least 10-15 minutes early; however, this is more of a general recommendation than a strict requirement. In any case, as long as you are within close proximity to the train, you should see an on-screen prompt letting you know that the event is about to begin and asking you if you would like to participate.

When the Spooky Carriage brings forth, it will follow a pre-laid out course to its inevitable objective. Again, you can simply meet the Haunted Carriage on its way to its destination or wait for it at the final stop, but it's better to follow the carriage as it moves along than to only take part in a small portion of the event. Here is a map of the carriage's route through the area, courtesy of Wowhead, for your reference: Once you've located the carriage, it's time to take part in the event itself.

Guards will occasionally attack the Haunted Carriage as it moves along its designated path. The skulls on the map above show where those guards are located. Although the exact location of their spawning may vary, you will typically come across them in that general area.

Even though the guards aren't very tough, especially if you're in this event with other players, they're a good source of gold and gear drops. To participate in as many of those guard fights as possible, it is generally recommended that you follow the carriage along its entire route cheap Diablo IV Gold.