Versus
The overgrown remains of a beautiful church and its environs, Mercy is a large and open level. There are two key locations on this level, the first being the northern balcony that covers the entire courtyard; it features either the Mortar or the Oneshot. The second is the bombed-out church to the south, which contains the Digger or Boomshot. The church roof is open to Mortar fire, so be careful of your position if you know the Mortar is active.
The northwestern cellar provides limited cover from enemies on overwatch at the balcony, as does the northeastern bell tower. The center courtyard is a killing ground—try to avoid moving through it as much as possible.
Horde
Command Post South, Sanctuary
This southern post has an ill-placed sentry within the church pews, and a single turret and decoy out in front. Many wall emplacements create an arc from the east to the west around the center courtyard, but maintaining them all is very impractical.
Focus your money on the turret and a few key walls at the entrances to the east and west. Then save up your money for repairs and the Silverback, if it’s unlocked. The lines of sight to the east and west are quite poor because of the arms of the church. Be prepared to move out into an exposed position to get a good line of fire onto incoming enemies. Stay alert and warn your teammates of dangerous enemies attempting to flank.
Command Post Southeast, Seaside Spawn
The two turrets and two sentries here provide good coverage of both the south center and the north center. However, both are fairly exposed to incoming fire, so prioritizing dangerous targets and taking them down quickly is important. The lines of sight for friendlies not on a turret are rather awkward. Foliage obscures many sightlines, so be prepared to fire even if you don’t have a clean shot. After the turrets are active, set up the decoy to draw fire when enemies get into close range. Boss waves can be challenging, as there is little blocking terrain to funnel them. This means you can be hit from any number of directions. Be ready to use the southern church as a fallback if you need to retreat. Or send someone north to pick up the power weapon and bring it back on an X9 round.
Command Post Northwest, Cellar
This position has an excellent vantage point, providing clear lines of sight to the north center and south. The turret has good coverage of the south center, and a few walls provide some protection from enemies getting into close range.
This location’s main disadvantage is that, if enemies get inside the cellar, you have very little room to evade. Furthermore, escaping exposes you to any remaining enemies in the wave.
Command Post North, Balcony
This location provides an excellent vantage point on the map. However, it is ill served by a poorly located turret on the northwestern side. Two decoys, one near the turret and the other on the upper platform, beside the Oneshot/Mortar spawn point, don’t offer much consolation. The northern side is relatively secure as long as the turret and decoy are standing. However, the turret gunner must have a protector to defend against enemies coming through the northwestern building.
The eastern side is much weaker, with no decoy or turret present on the ground level and just a single sentry. The remainder of your troops should cover this approach to ensure no Horde sneak past the wall positions via the gallery on the eastern building. A fair number of barrier positions are here, but try to activate the western turret and decoy first.
Beast
This is a very difficult Beast map, as the wide-open central courtyard area is a killing ground for Locust forces. Try to exploit the ranged attacks that the Beast forces possess: Savage Drones, Kantus, Savage Grendiers, Boomer, and the Savage Digger.
If the COG forces spawn in the chapel, expect them to rush your spawn point—be ready to defend at close range if this occurs. Try to coordinate your assaults on the COG bases. Use the little cover that’s available to approach, and then strike as a single unit to inflict as much damage as possible.