HT Games
Instructions
Go through the level, destroying everything in your path with both Scarecrow's Bi-Plane and Joker's Helicopter. Try not to lose any hearts so you are in full health when it comes to facing the boss of this level: a police helicopter. Note that if you don't pass this level, you won't be able to use the Joker's Helicopter or the Scarecrow's Bi-Plane in freeplay.
Destroy as many of the turrets and small police helicopters surrounding the boss first so you can avoid being hurt by these. This will lessen the number of bullets coming toward you.
Grab the mine sitting on top one of the buildings to the left of the boss with Joker's Helicopter. Toss the mine onto the billboard-looking object directly behind and to the left of the boss. This will cause a turret to come out of the building and start shooting at you.
Shoot the turret with Scarecrow's Bi-Plane, and then the turret will start shooting the boss, causing the boss to divert its firepower away from you.
Grab a second mine that appears in the same location as the first. Again, grab the mine with Joker's Helicopter and throw it on the billboard behind and to the right of the boss.
Shoot the second turret that appears with Scarecrow's Bi-Plane to divert its firepower toward the boss and wait for the boss to take down the second turret. By now, at least three of the boss's six hearts should be gone.
Shoot at the boss to finish off the last three hearts. When it dies, you'll have passed the level. At the end, there is a short video and the game announces that you've unlocked freeplay for this level and that you've unlocked both Scarecrow's Bi-Plane and Joker's Helicopter.