Risk of Rain 2’s many stages are covered in Shrines you can interact with to influence the game. The Shrine of the Mountain, pictured above, is a single-use shrine that will bump up the difficulty of that stages boss fight. Instead of a single boss to fight, you will need to take on two of them.
Why would you do this? Because successfully beating them will also result in double boss loot! It is a great way to take advantage of the calm early game, and earn more items when it is pretty safe to do so.
The Shrine of the Mountain looks a lot like a skeletal hand sticking out of the ground, trying to form a fist. If you see a Shrine and run up to it, it will tell you which type it is, just be careful not to accidentally hit E and use a Shrine you don’t want!
The Shrine of the Mountain is also tied into the Ascendant Challenge. If you activate two of them at the same level, then beat the bosses, you will have achieved the Ascendant Challenge, and unlock the Royal Capacitor Item. The Royal Capacitor is well worth chasing, as it can call down a bolt of lightning that will do considerable damage to a single target.
Finally, you can use the Shrine of the Mountain to help you get the Deicide Challenge. To do this, you need to defeat an Elite boss on Monsoon difficulty. Using the Shrine will help with the possibility of an Elite Boss spawning, but if you manage to find three in one level, then it is pretty much guaranteed.
Getting the Deicide achievement will unlock the ridiculously powerful Brainstalks item. Brainstalks will completely remove your skill cooldowns for 3 seconds after killing an elite monster, meaning at higher difficulties, when Elites are more common, you will become a DPS monster!
Now, that should cover everything you need to know about the Shrine of the Mountain. Best of luck on your next run!