Get the heart monitor from the first level. Here's how if you missed it


Go to the first level
Head north through the first bottleneck
Hug the right wall until you come across a cave entrance


Go into the cave
There is another cave. Go into that one


Put on the mask with "v"


See that every heart signature (even dead stuff) is marked by a red dot. This will be useful later

Once you're done hunting all the boars you like in level 1, head on to level 2. Bullet upgrade is not required for killing the boss

On the second level, head west until you hit a wall.
Cross the stream to your right and observe a hidden path between the brush and the mountain.


If you put on your heart visor, you can see there are two heart signatures in the distance.
Approach the signatures until the corridor opens up.
You should see the rock that the boss is sleeping on. You can make as much noise as you want; it won't wake up until you get near

You can even move around as much as you want as long as it's in the lower area


Look at the south cliff face and find the dent that you can climb up



Practice running into it so that you climb up it (don't crouch). You should be pretty high in the air (there is an invisible ceiling though, I think)
When you release all movement controls, if you did it right, you should just fall back slightly into a stable position
This is where you can cheese the boss


Go run up to the heart signatures. Keep moving towards until your compass starts to spin. Once that happens, run back towards the cheese spot and go all the way up it until you're in the stable spot

Look down. If you did it right, there should be no boss. Instead, he should be right above you. Don't worry though. He can't get you (as far as I know)


Turn on your heart visor again. You should see he has two hearts. You gotta shoot both to kill him


When you're all the way at the top, you can't look up enough to shoot him unfortunately. To reset his pathing, inch backwards a little. He should come running around to below you. If he gets too close, just back up again.


Try to shoot him in his hearts while he transitions between the two spots. It will take some learning, but you have a lot of time!


That's it for my guide. I hope it helped