A vet appointment is a good thing to get as soon as possible. The tail deffinitely looks infected and dying off near the tip. This can be caused by several things. Skin not shedding off the tail tip properly, can cut blood circulation causing the tail to die off. Injuries to the tail (bites from other dragons, damage from cage decore falling or pinching the dragon, cricket bites (this is more likely if the tail was bit or injured before hand, giving the crickets access to non scaled covered areas).
Till you see your vet, I suggest moving the dragon onto papertowel to prevent sand etc from sticking onto the tail. Give the dragon a soak and gently wash the tail with a milk non perfumed soap (very dilute) or a diluted beradine solution. The soak will also help loosen any unshed skin off the tail and dead parts may fall off. After the bath, apply neosporin (or other antibiotic ointments lacking any pain killers) to the affected areas of the tail. This will help kill bacteria. Your vet should do bloodwork to get a better ideal how intensive the infection is, and may prescribe anti-biotic injections to fight the infection from the inside.
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PHLdyPayne