Throwing Jars at Doors
When you first enter the Key Cave, the door behind you closes and you appear to be locking inside the dungeon. Pick up a jar and throw it at the door. It will open, allowing you to leave. Later in the dungeon, another door will close behind you. Pick up another jar and throw it at the door to open it. Try this trick whenever a door closes behind you in a room where jars are available. If jars are not available, you must find another way out of the room.
Enemies
This cavern features several new types of enemies. The first ones you encounter are the red Bombites. Hit them with your sword to send them reeling away. They may bounce off of a wall and back at you, so equip your Feather and use it to jump out of the way. Pairodds are the bird-like creatures that teleport around you. Use projectiles like arrows to take them out. The snake-like creatures are Dodongo Snakes. Set bombs in their path and they will eat them. Three bombs will defeat them.
Puzzles
You must solve several puzzles to progress fully through the Key Cavern. In the first room, a treasure chest will appear only after you have defeated all of the enemies. In the room with the Dodongo Snakes, defeating them makes a portal appear. Go through it. The blocks that are blocking your path to the treasure chest are able to be pushed. Walk into them to move them out of the way. Open the chest to receive the Pegasus boots. Equip them with either the "A" or "B" button. Hold down that button to charge up and run forward.
Boss
Equip the Pegasus boots that you found earlier in the level. Use them to ram into the wall. This knocks the enemy Slime Eyes onto the ground. Attack him with your sword until he begins to split into two creatures. Use the Pegasus boots again to slice him in two. Attack the two Slime Eyes with your sword until they are defeated. When the Slime Eyes jump into the air, equip the feather and use it to jump whenever they are about to land. If Link is on the ground when they land, he will be stunned for a moment.