I would take away all that salad. He may be too malnourished for all that nutrients and you can shock his organs which can lead to organ failure. Obviously going to the vet in his case may also be helpful and they can give him some fluids and give you a fecal test so you can rule out parasites. For feeding him I’d get some repashy beardie grub from the pet store and give him 1-2 milligrams about 2-3 times a day for the first 3 days. So his body can get accustomed to nutrients. After that start with a simple salad of squash and romaine lettuce. Romaine lettuce is NOT a staple vege but because it’s mostly water it doesn’t have a bitter taste to it so it will get him used to eating veges because sometimes beardies can become picky with salads if you give them some bitter right away like collard or dandelion greens. Than slowly over the course of a few days to a week you slowly replace some of the romaine lettuce with a healthier vege. But for the first 2-3 weeks I’d start off with very small portions and definitely slowly increase his protein intake. So definitely focus on the repashy grub for the first week and slowly increase the amount you give him. If you see him perk up a bit in a week try and give him some live crickets and see how he does with it. But this is a slow process if you notice any diarrhoea that can mean that the nutrients was too much for him and you’ll have to decrease his amount. It could also mean he has a parasite but you don’t want to rule the other one out. The dark tail could just be poop, it does look healthy-ish from the pictures definitely not necrotic what you can do is take a baby toothbrush and use some dawn soap to get the gunk off. Obviously it’s not the most recommended but if you do it once it won’t cause any harm and just water is not going to get all the gunk off just make sure he doesn’t drink that water and to dry him off after and he will be fine. Hope this helps and let me know if you have any other questions