“No need to sign for this package! Dropped from the sky, it deals Area Damage to enemy Troops before delivering a Royal Recruit. The empty box is also handy for espionage.”
The Royal Delivery card is unlocked from the Spooky Town (Arena 12). It is a defensive Spell played on the player's own side. The Delivery drops from the sky, damaging air units and ground units. Once the delivery has hit the ground, it spawns a single Royal Recruit. A Royal Delivery card costs 3 Elixir to deploy.
The spell has a three second delay after being deployed. Keep this in mind when defending, and time your drop accordingly. This is especially important against the Goblin Barrel. As soon as you see the Barrel coming, place the Delivery right on top of your tower to prevent all damage.
While the spell itself cannot be played past the bridge, it has just enough range to hit a Princess that is standing at the bridge.
The spell is effective at dealing with a Miner swarm combo. Wait for the swarm to get closer to the tower, then drop the Royal Delivery on it. The spawned Recruit will then help deal with the Miner.
Placing it directly on ranged glass cannons such as Musketeers and Wizards right after they cross the bridge will allow the Delivery to counter these troops for a positive Elixir trade. The player should make sure that the enemy troop is in range of your Princess Tower when the Delivery drop, and they should avoid letting the enemy troop lock onto the tower for unnecessary damage. A workaround to this is placing the Delivery right in front of the troop. This will push the enemy troop back slightly and force them to retarget onto the Recruit if the spell deployment was too late.
The spell pairs extremely well with Bomb Tower or Goblin Cage on defense. The building will buy time for the Royal Delivery to drop as well as clumping up all the enemy troops, and the spawned Royal Recruit will distract the remaining enemy units long enough for the Bomb to blow up or the Goblin Brawler to finish them off.
On 3/8/20, a Balance Update increased the damage of Royal Recruits by 8%, and also removed the Delivery's knockback. Its description was also updated to reflect this, previously saying "No need to sign for this package! Dropped from the sky, it damages and knocks back enemy Troops before delivering a Royal Recruit. The empty box is also handy for espionage."
In the card's description, "the empty box is also handy for espionage" is likely a reference to Metal Gear Solid.