Voices in the wind say that soon the Hivefleets will descend upon the cities of the Imperium using a variety of strategems and trickeries such as the ones listed below:
Superior Concealment: Deployment Stratagem
Lictors are the ultimate terror weapon in the Tyranid hordes, lethal creatures capable of ranging independently ahead of the Tyranid force to wreak havoc behind enemy lines. The urban sprawl of a cityfight provides Lictors with unparalleled opportunities to hide from the enemy, springing perfect ambushes that leave the enemy with no chance to react!
After deployment areas have been established, but before either player deploys any models, the Tyranid player may place D3+1 Concealment markers anywhere on the board. If a Lictor (including Deathleaper) enters play within 3" of one of these markers it may charge on the turn that it arrives.
Gargoyle Eyrie: Key Building Stratagem
Gargoyles will occasionally choose a high place within a city from which to launch their attacks. Unsuspecting enemies will venture into these chosen ruins, only to find themselves beset by dozens, if not hundreds, of screeching, flapping Tyranid creatures, who erupt from quiet corners and hidden spaces to soar up and out across the battlefield.
The Gargoyle Eyrie stratagem is always the tallest building on the battlefield and is declared after the terrain has been set up, but prior to deployment. If your army includes any Gargoyle Broods, they must start in reserve and Deep Strike onto the battlefield anywhere within 12" of the marked building. Additionally, when a unit of Gargoyles enters play through Deep Strike, any non-Tyranid units inside the building suffers 3D6 Strength 2, AP- hits and must immediately fall back.
Pheromone Clusters: Deployment Stratagems
Seeded across the battlezone by stealthy Tyranid creatures, Pheromone Clusters are an unpleasant excretion that acts as a potent lure to Tyranids. Even Raveners burrowing below the ground and Harpies soaring high above the combat zone are drawn inexorably to the pungent alien secretion.
After deployment areas have been established, but before either side deploys any models, the Tyranid player may place D3+1 Pheromone Clusters anywhere on the board. Any Tyranid unit that attempts to Deep Strike within 6" of a Pheromone Cluster does not need to roll for scatter.
Ground-burst: Dirty Trick Stratagem
As Trygon and Mawlocs burrow through the sewer networks deep below the city, they are occasionally retasked by the Hive Mind, temporarily despatched from their frenzied tunnelling to burst through the ground floor of a building, throwing the occupants into chaos, before continuing on their way.
The Ground-burst stratagem is declared at the start of any turn except the first. The Tyranid player chooses a single building - all models on the ground floor of that building must immediately take a Dangerous Terrain test (vehicles will test as if they had moved more than 6"). The ground floor of that building then counts as dangerous terrain for the remainder of the battle.
When is the last time you guys played a game of Cities of Death?.