What is this? Should I be worried?

[SteveCGY]

Just noticed this sprouted on a piece of rubble in my display out of no where. Just wondering what it is and if it's good or bad. Tried my best getting a picture.

[denny_C]

ball anemone( actually a mushroom) they are fairly harmless( that species anyways) but do pack a powerful sting , they are completely nocturnal and often done hang around the light unless they are in the path of food

[denny_C]

could also be a strawberry but it doesnt quite look like it

[SteveCGY]

So it's safe to keep and see what it does? It seems happiest under my bubble coral so it has like an umbrella over it.