Heart piece 13 is inside of the Forest Maze. Get Will and then go back and go to the room on the west end and enter it. Heart piece 14 can be earned in Middle School by shooting out all five of the red bells that are on the walls.
Heart piece 15 is earned inside the Forest Maze dungeon by shooting out all five of the bird houses and destroying them. For heart piece 16, go to the public library dungeon. Search for the overdue books. There are five total. Find them and then go back to the entrance and open the green chest.
Heart piece 17 is inside of the Lab Bunker dungeon. You have to destroy the five specimen jars in order to find them. Heart piece 18 requires the Robot Toy which is inside of a brown roofed house near the middle school. Go inside and use Nancy to break the wall open and get the toy. Give the toy to the clerk at Bradley’s Big Buy Store, which is the one just to the northeast of the middle school.
Heart piece 19 requires you to have Mike. Take him to the Sattler Quarry, which is on the far southeast end (Far East of Hawkins lab) and jump the ramp. Follow the cave, then use Nancy to break open the blocked one and inside will be the heart. Heart piece 20 comes from Tommy. Find the pocket knife behind the house with the swimming pool behind it, then take it to Tommy, who is in front of the high school.
To get heart piece 21, get mike and jump the ramp to go to the dump and find the bottle of pop (yes, it’s soda, but the show is set in the midwest). Then give it to Tommy. For number 22, buy the hairspray at Bradley’s Big Buy Store for 100 coins, then take it to Carol at the High School and she will give you the heart piece.
For number 23, go to the sewer with will and go to the southwest corner and go through the pipe. Get the lipstick, then take it to Carol at the high school. For number 24, find the keychain at Castle Byers in Mirkwood Forest, and then go find Joyce and give it to her.
For heart piece 25, go to the general store east of the police station and buy the phone, which costs 50 coins. Then deliver it to Joyce, who is at the Byers’ house. For number 26, get the cassette tape from the middle school, in the northeastenmost room. Then go to the non-dungeon forest outside of the Forest Maze. Once you’re there, find Jonathan and give him the tape.