The monsters you encounter here are solely determined by your total Monster Level increasers.
The extra ML caused by the rain depth during the Heavy Rains challenge path is not taken into account to determine the monsters you encounter in this zone.
To finish the quest on this peak, you must reduce oil pressure by defeating the monsters. The pressure starts at 310.66 µB/Hg (microbowies per Mercury).
Wearing dress pants increases the pressure reduction of each kill by 6.34 µB/Hg.
+ML
Monster
Pressure reduction per kill
Number to kill to finish quest (without dress pants)
Initially, the Rabid Dogwood from the Florist Friar did not affect which monster was encountered. This was fixed during May 2013.
References
The name of this adventure location refers to peak oil.
The unit of oil pressure, µB/Hg (microbowies per Mercury), refers to the song "Under Pressure" by David Bowie and Queen.
The message with low stats refers to the movie There Will Be Blood, about oil greed. It also refers to the phrase blood for oil, a protest slogan about the American-Iraq War.