I have been searching for this title since the movie was misplaced long ago but I cannot seem to remember the title of the movie and random searches have come up with nothing.

The cartoon movie is based on this painter that ends up taking a nap under an enchanted tree that grants him the ability to talk to the woodland animals and also enchants his paintbrush. The main antagonist is a evil king that has a watermelon looking torso covered in spikes.

As the story progresses, the painter (after assisting the animals of the forest a few times with his paintbrush) realizes his powers are fading. He takes a few animals to the Spike Castle (not actual name... it is what it looks like) in attempts to feed the evil king a magical potion that would turn him good. Right towards the end, the Painter could no longer use his paintbrush and cannot speak to the animals anymore, but was successful in making the king drink the potion right when the king woke up and snarled. He then turns (this part is funny) pink and the spikes turn to flowers and he becomes a good king of the forest. Unfortunately, a teary goodbye at the end since the painter must leave.

I need to find out what this movie is so I can find it again. It was actually really fun to watch as a child, and now being a bit nostalgic would like to see it again.

The Elm Chanted Forest (IMDb page)

I just wanted to say that I've been searching for the name of this movie for years - and this is the first time anyone else has mentioned it.
It was my favorite movie too as a kid - great times!