Under the right care and conditions, your plant will grow happy and healthy. But here are some issues you may encounter while caring for a Euphorbia:
Scale, mealybugs, fungus gnats and spider mites - When spotted, wash these pests off using cotton swabs and water.
Sunburn - While they love light, they can turn yellow or brown from too much direct sun. Move the euphorbia away from its light source to cool down.
White/grey powdery film - This is due to mildew which is a fungal disease. It is caused by high humidity, poor ventilation, insufficient light and/or lack of nutrients. Applying neem oil is a good way of eliminating mildew.
Root rot and fungal disease - This is due to overwatering. Err on the side of under watering as most of the time you can bring them back from dehydration without issues.
Wrinkles - This is a sign that your euphorbia is very dry and a soak-watering is necessary. After watering, be sure to empty excess water and not let it sit in water.
Handling spikes - Use leather work gloves or kitchen tongs to gently handle the spikes and to avoid the pricks.