This gated cemetary, surrounded by tall wrought-iron fencing, is haunted at night by a pack of undead. The PCs might be sent here to put them back to rest, or perhaps they're passing through on their way to some other objective.
The undead only haunt at night, so the battlefield should be shrouded in darkness. If you want a bright moon to provide some illumination, make it shadowy instead. There are no torches or lanterns lit here.
Battle begins when the PCs enter the cursed graveyard. The iron gate suddenly lurches shut behind them, locked tight, and the moaning of undead can be heard from within. While it's possible to get the gate back open or scale the fence to flee, such endeavors would take sufficient time that the undead would strike blows; if the PCs want to avoid injuries, they'll have to defend themselves.
Sections marked M are mausoleums. These are walled on all sides; phasing is required to occupy those sections. Entities within a mausoleum cannot target or otherwise affect entities outside and vice-versa.
0 0 <-- PCs start in either of these sections 0 M 0 0 0 0 0 0 M 0 0 0
Enemies will wait for PCs to advance deeper into the cemetary before they attack. Zombies will advance to the central row and wait there until they can move to attack. If the PCs are able to see in the dark or illuminate at range and start taking shots, all undead will move and attack as aggressively as possible.
Apart from waiting for the PCs to venture deeper within, the undead use no particular tactics, typically attacking the closest foe. The Mournful Ghosts do prefer to go after lone PCs however, hopefully avoiding blasts from the Resentful Spirit or explosions from Crawling Corpses. The undead do not try to prioritize attacks based on perceived PC threat level, and the Crawling Corpses will not try to crawl out of melee.
The undead are simply dead once more. If this was the PCs' mission, they can return and receive whatever reward was promised. You may give them the opportunity to rob the mausoleums of any valuables inside; each PC that choses to engage in this behavior gains 1 Wealth but loses 1 Karma. You could extend the ghostly adventure by having stairs inside a mausoleum lead into ancient catacombs further infested with undead.
The PCs must flee the cemetary by climbing the fences or forcing open the gate. Each suffer an Injury in the process. You might call for an Acrobatics roll vs. 1d6 to avoid a second injury from scaling the fences.
For a truly cursed encounter, you could make the cemetary impossible to escape. That makes this a battle to the death; a defeated PC can spend 1 Karma to regain 2d8 lost HP (and can take their full turn).
If you want a long-ranged threat deep within the cemetary, consider a Hobby Lantern. This would take the place of a Resentful Spirit, Zombie, and Mournful Ghost, so it's best used with higher player counts. An alternative could be a Necrophyte if you want an individual to be responsible for the haunting; it's worth 1.5 PCs, so you have several choices of what to remove to add one. For a higher undead count, you could instead try putting in several Ectoplasm Bulbs, which could swap at around 2 for 1 with the Resentful Spirit, or 3 for 1 with a Crawling Corpse.
For extra flavor and a little extra challenge, have all the PCs' light sources be extinguished the moment the gate slams shut. So, the PCs start the scenario in total darkness. They'll have to spend some plays getting their light going again (they can still start with such Gear equipped, and they can be re-lit with no difficulty). If you do this, consider having the undead go ahead and attack in the first round so the PCs can't safely hang back and recover lighting before continuing on.
Another option is to wait until the PCs are deep within the cemetary before the gate shuts and the undead appear. In this case, the PCs should start based on their narrative position as they explored around; if not detailed, have them start in the central two sections between the mausoleums. For a truly dire starting situation, combine this with the previous paragraph's adjustments.