Hi Justin, welcome to GrowsOnYou.com. Looks like you have a major infestation of white fly. Spray daily with organic dish soap solution. Or, you can swab the entire plant with a cotton ball/swab dipped in hydrogen peroxide. Do this several times over a few days to be sure you get all of them. This is more of symptom though. It could be lack of sufficient sunlight and air circulation.

Move the plant to more sunlight. The sun's UV rays will naturally fend off these pests. Open a window so the plants get a good airflow. Wind also deters these flies. Don't over water either. Let the soil dry out between watering. These are the long term remedies I opt for over caustic pesticides which only 'clear the decks' for the next round of bugs.

It's hard to tell from the picture and I don't know what pests and diseases you have 'Down Under' but from what I can see, it looks like scale insect. If this is the case, then a systemic insecticide will sort it out. This and red spider mite are always a problem if the plant in question happens to be indoors. You must get one that will deal with scale insect as some don't. The only proviso is that you won't be able to eat the fruits. Having said, only a guess.

I thought scale insect too. I've used methylated spirit painted on the affected places and its very effective but it would be a long job with an infestation this bad. I wonder if you could spray meths onto it, being very careful not to breathe any spray. If you can still get Malathion in Aussi that works well but its banned in the UK now.

The infestation is so bad that I, personally, wouldn''t treat the plant at all. Bin it and buy a new one.

I agree with Bulbaholic, bin it as you will be there forever getting rid of the scale bug :o(

My money's on scale insect too - the black leaves are likely black because of honeydew deposits, which creates the right conditions for sooty mould on the leaves - get rid of the scale and the sooty mould should clear.As far as the toadstools go, they're just from mycelium present in the potting soil - hard to say whether your plant needs repotting or not because we can't see it all. The fungal growths might be an indication of overwatering, but otherwise (not being able to see the toadstools) are likely just the fruiting bodies of the mycelium. Did you use sterile potting soil in the pot?

Black scale is sometimes an issue in your country (note that the scales can be black or brown) - this is a pretty bad infestation, but obviously, we can't see the whole plant, so depends how extensive the problem is as to whether you treat for it or just dispose of the plant. Info here , you'll need to copy
and paste into your browser http://www.oliveaustralia.com.au/Olifax_Topics/Black_Olive_Scale/black_olive_scale.html

The yellow fungus indicates a problem with the root system. I'd follow Bulbaholic's advice too but still find out why this happened in the first place. Somewhere the plant's requirements werent met.