Subtle Curfew is the fifth stage in Stairway to Darkness, sub-chapter 21.
The units that are highly recommended for this stage are Crazed Dragon and King Dragon Cat since they both outrange Angelic Slepnir and if you have any other cats that can outrange him you can use them as well.
This level becomes easy after the player has stacked enough long range attackers. Note that Pigeon de Sable can make shockwaves, which can damage all units in a range of 467. Bahamut, Ururun and King Dragon will be damaged!
Therefore, it is recommended for players to kill Pigeon ASAP. Otherwise it will be better for players to have cats that have higher range 467. Shockwaves, If you have units that have shockwaves and outrange Slepnir, Pidgeon will be killed this way.
Any meatshielded shockwave blockers work wonders against the Pidgeons.