"There are TOO MANY BOOMERS IN THIS MAP!"
This is a port of the "Devil Mountain" campaign from L4D2 ported by brumans.
Port is not an exact copy of the original, various changes have been made to it to work in L4D1.
https://www.gamemaps.com/details/31209
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https://www.youtube.com/watch?v=xnQJv_4Ws-o
A very rare type of takedown achievement tactic known as "Splashdown" which is very difficult to trigger and requires you to be very close to the water then ram the AI cop or racer opponent towards the water without you falling with them to trigger this, which will result in a few tries.
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https://www.youtube.com/watch?v=PmKPqZAUmRw