Q.Fungus
How to get rid of fungus on the elephant ears, & stop it from coming back also is mulch bad for them??

Avoid overhead watering and water splashing unto the leaves.
Mulch should be kept at least 6 inches from the base of the plant.
Make sure the plants have air circulation around them.
These articles will help you with treatment options.
https://www.gardeningknowhow.com/ornamental/bulbs/elephant-ear/elephant-ear-brown-edges.htm
https://www.hunker.com/12003917/elephant-ear-diseases