"Amateur Surgeon 2" has a mystery boss at the end of the second act called Dwayne Pipe. He has several bugs living inside of him and it's up to you to get them out without killing him. There are two different sizes of bugs crawling around his insides and the larger bug can do significantly more damage. You need to keep his heart rate up while destroying each of the bugs in turn to successfully complete the surgery.
Complete the surgery until you see a thick yellow line appear on Dwayne's heart. Use the pizza cutter to slice through the yellow line and get inside of his heart. There will be a small bug running around.
Use the chainsaw on the red rear segment of the bug. The red segment will move up one space on the bug after you destroyed the first one, so continue to use the chainsaw on the red segments until the bug is completely destroyed. Use the needle to restore Dwayne's heart rate if necessary. Use the vacuum to suck out the poisonous green pieces of the destroyed bug.
Cauterize the small cuts in this area using the lighter, then use the gel to soothe the cuts. You'll notice a rumbling sound before a giant bug head pops out of the inside of Dwayne's heart. Use the chainsaw or the car battery on the middle of the bug's face while it is roaring at you. This will daze the bug's head and will cause it to retreat. Use the needle on one of the three eyes of the bug to get it to retreat completely. This will cause another small bug to appear.
Destroy the bug by using the chainsaw on its vulnerable rear red segments. Vacuum up the poisonous bits of both the destroyed smaller bug and the damaged larger bug. Close the large wound in the center of the screen by using the needle. Then, use the lighter to cauterize the large wound and the smaller wounds and use the gel to soothe them. You'll hear a rumbling noise again indicating that the larger bug is about to appear.
Stun the large bug by using the chainsaw or car battery on the inside of the large bug's mouth. Use the needle on another one of the eyes of the large bug to get it to completely retreat. This will cause another smaller bug to appear. Use the chainsaw on the red rear portions of this bug until it is destroyed, then use the vacuum to suck up the poisonous bits of both bugs.
Close the large wound in the center of the screen by using the needle. Again, use the lighter to cauterize that wound and the smaller cuts, then use the gel to soothe all of the wounds. You'll hear a rumbling again indicating that the large bug is about to return. Use either the car battery or the chainsaw on the center of the mouth of the large bug until it is dazed.
Kill the large bug completely by using the needle on the third and final eye of the large bug. This will cause three smaller bugs to appear. Kill each of them by using the chainsaw on their red rear segments. Vacuum up all of the poisonous bits of the defeated bugs. Close, cauterize and soothe all of the remaining cuts to finish the surgery.