The Acid Rain is one of the four upgraded crossbows. When this bow is shot, an initial explosion is produced which kills all zombies in its blast area, following which, acid rain falls from the sky for a short amount of time killing any zombies nearby. This crossbow is useful in high rounds for camping strategies.
An interesting point to note is that the Acid Rain will always produce headshot damage, which is also useful for earning cash ($100 per kill) as compared to the other bows which count as an explosive kill, only netting $60.
However, the effect of acid falling from the sky is slighty obstructive which is its only (albeit small) downside.
How to obtain
The player must first find a small Owl statue located around the map. Like the other statues, it shares a random spawn location. After acquiring the statue, the player must head to the recreation area and place the statue by the speakers.
The player must now damage zombies to about 30% of their health and allow them to be "absorbed" by the statue. After enough zombies are damaged, the statue will be completely charged and will be able to be picked up.
After picking up the statue, head over to the Cabins, and place the statue next to one of the Owl statues. The player must now kill about 20 zombies with the Vlad near the big statues. Killing zombies at any of the two statues will count towards the bow. After enough zombies are killed, the statue can now be picked up, and once the player does so, the player's Vlad will be replaced with the upgraded Acid Rain.