The final boss in the Forbidden Woods dungeon is called Kalle Demos. The boss is a giant plant that has large tentacles with which is uses to attack you. This boss is quite easy to beat, but you will need to be quick with your boomerang in order to kill him quickly. Here is what you need to do to kill the Forbidden Woods dungeon boss, Kalle Demos in the Wind Waker.
By the time you get to this boss, you should have had enough time to get the hang of how the boomerang works, so I will work off the assumption that you already know how to use it.
Start by walking over to the plant in the middle of the room as this will trigger the fight to start. Right away you will see that the boss attaches itself to the ceiling of the room with blue tentacles. These are the weak points that you need to target with your boomerang. You can target up to 5 of them at a time, so try your best to get the most out of each throw. As you are targeting them, the boss will be shooting tentacles through the dirt to hit you and will also try and slap you with the larger tentacles. Make sure you keen an eye out for these so you don’t get hit.
When you break all of the tentacles that are attaching the boss to the ceiling, he will fall to the ground and expose the little plant in the middle. Run over and attack this with your sword until the plant swallows you and spits you back out. Repeat the same process to knock him off the ceiling again and keep doing this until he is dead.
This boss doesn’t have many surprises, so if you stick to the above tactic you should wipe him out very quickly. If you get stick for health, cut the grass with your sword and it will drop a heart 9 times out of 10.
Here is a video of the boss fight, in case any of the information above was unclear.