So, the movie is a cartoon from the 80's that has a guy in it who is a painter/artist.
The guy ends up going into one of his paintings, and ends up in a weird world.
I think there are talking mushrooms in this painting world. That's pretty much all I remember about it. Thanks!

Is this something from your childhood? The only thing that pops into my mind is a movie that is mostly animation but it does mix with the "real world". Cool World (1992).
Gabriel Byrne plays a cartoonist/artist who falls into his creation. He is given some sort of drug by his cartoon creation played by Kim Basinger. Other "toons" take drugs and booze in this world too. Brad Pitt is in the movie as well. If this is not what you are thinking about, it is something worth watching. Fun movie.

Thanks for the reply! I actually ended up finding the movie I was looking for. It is called Elm-chanted Forest. The one you described sounds pretty cool as well. I will definitely check it out! Thanks a bunch =)