Mushrooms?!? What to do with them?

Mushrooms?!? What to do with them?

I have a large container with a gardenia surrounded by pansies. One of the pansies hasn't been doing well. Many of it's leaves have turned grayish or speckled with white dots. I think this is some type of fungus or mold. More recently the leaves of my gardenia have been turning brown and dry in some areas (which may or may not be related). This morning I noticed mushrooms growing next to the the pansy! I know some mushrooms are helpful to your plants, but are there some that can hurt your plants? I don't want to spread any diseases throughout the whole container, so should I dig up the diseased plant and toss it?
New house – New garden

New house – New garden

Plant ID Please

Plant ID Please

The bishop

The bishop

My New Apartment

My New Apartment

Wall of Frames

Wall of Frames

My Bedroom

My Bedroom