Abrasions on succulent are not serious. Typically, the plant will grow out of the spotting. This occurs when sensitive succulents are handled by their leaves. To prevent this, try to avoid touching the leaves. If you are handling cuttings, grab the plant from the stem instead.
Although there isn't a ton of information on this disease, it is not serious. It is believed to be a fungus most commonly found in Haworthia and Gasteria plants. Placing your succulents in an area with good air circulation will help prevent this disease.
With most succulents, when they change their colors from green to red or green to a more vibrant color, the leaves sometimes appear blotchy. This is completely normal and the plant should grow out of it once the color change process is complete.
DEAD LOWER LEAVES
Losing lower leaves is normal if the center growth is healthy. As long as you are seeing new growth at the top of the plant, it is healthy. In some succulents, the lower leaves die off to protect the stem from harsh sunlight.
Plant rot is very serious in succulents. This disease is a result of over watering. Once a plant receives water, it stores enough in its leaves to survive. The excess water absorbs into the soil, causing the roots to rot. A sure sign of plant rot is a mushy black/yellow center. In most cases, the plant is not salvageable.
Sunburn occurs when plants that haven't been acclimated to full sun are introduced to it. Most commonly found on new plants, sunburn sets in when the weather changes from cloudy to bright and sunny. Sunburn also occurs when a plant is watered while sitting in a very sunny/warm spot. Try watering in the evening or morning. It is not fatal, but is cause for more diseases.