Complete guide for Is This Undertale (Version 0.10).
Heart Locations
Purple Heart
Enter the teal archway. Take the right path and go right until you loop around to the path behind the world entrance. Go up onto the bridge and interact with the heart on the top.
Blue Heart
Enter the teal archway. Take the north path, go up and step onto the bridge. Go up the bridge and take the first exit on the right. Go right again then go down the path between the cave pillar and the tree. Interact with the heart in the minecart.
Orange Heart
Enter the gray archway. Go up from the entrance and interact with the heart floating in Grillby's entrance.
Green Heart
Enter the gray archway. Go north-west from the entrance and enter the forest. Go north inside the cave to reach a river. Interact with the boat. Go south and interact with the heart in the path.
Cyan Heart
Enter the gray archway. Go north-west from the entrance and enter the forest. Go north inside the cave to reach a river. Interact with the boat. Go south to an area with multiple paths. Go left and enter the purple building. Once inside go right and through the door. Go right again and interact with the heart in the corner.
Yellow Heart
Enter the gray archway. Go north-west from the entrance and enter the forest. Go north inside the cave to reach a river. Interact with the boat. Go south to an area with multiple paths. Go down and interact with the heart.
Ending
Find and interact with all six hearts. Go to where the Yellow Heart is and the door underneath it will disappear. Go down and follow the shadowy figure until the screen fades out.