from what it looks like to me.
.The snail is a tropical abalone (A ferocious algae eater)
.the decayed head of the torch is not possible to bring back.I would give your entire coral an iodine bath.
.Chalice color changing possibly of light changes or placement in the tank,its fine and healthy looking.As long as it doesn't start to recede or skin flaking off.
.purple plant I am not of the name.the yellow looks like diatom.
.purple green and red looks like calcareous plants.
I am sure more people will chime in
