Well, his brothers would react with a sense of urgency. They would call for backup or medical help if needed. There would be a lot of concern in their eyes. They would probably have some internal dialogue about how they need to be more vigilant in the future. And they would be very gentle when moving Nightwing to a safer place, showing their care and love for him as a brother.
His brothers would likely be very protective. They might immediately go on the offensive against whoever hurt Nightwing. For example, if it was an enemy attack, they would fight back fiercely. They would also be concerned about his well - being and quickly try to assess the extent of his injuries.
Maybe Nightwing is trying to protect a civilian in front of his brothers. He jumps in front of a dangerous weapon aimed at the civilian. The weapon is some sort of experimental tech that causes a lot of internal damage. His brothers witness this selfless act and it stirs up a mix of emotions - pride in his heroism but also anger towards the attacker. They then have to deal with not only getting Nightwing medical attention but also hunting down the perpetrator.
Leo would likely take charge immediately. He'd assess the situation and start giving orders on how to help Mikey. He'd be calm on the outside but worried on the inside.
Yuki would likely be very concerned. He has a soft spot for Tohru and would probably rush to her side, trying to find a way to help. He might even blame himself if he thinks he could have prevented it. Kyo, on the other hand, would initially be angry, but that's just his way of showing worry. He would be more hands - on in getting her the help she needs.
Simon might be in a bit of a panic. Since he's her friend and also not as used to the dangerous situations as the other Shadowhunters. He'd try to do whatever he can to help, like getting help from more experienced Shadowhunters or trying to comfort Clary while she's in pain.
Macgyver would probably be very worried. He'd quickly assess the situation and try to stop the bleeding if she was bleeding. He'd use his resourcefulness to make a makeshift stretcher or bandage.
Beast Boy would definitely be one of the first to react. He and Raven have a special bond in the Teen Titans, so if Raven gets hurt, he would be extremely worried. He might use his shape - shifting abilities to quickly get to her side or try to find help.
Raph usually gets really angry. He blames himself for not being there to protect Leo or he gets mad at the enemy who hurt Leo. He'll be the first to want revenge and will be very protective of Leo while he's injured.
The other characters' reactions can vary. Pixal, if she's around, would use her technological knowledge to see if there are any internal damages to Jay, especially if it's related to his electrical components. The villagers of Ninjago might also show their support. They could bring food or offer shelter for Jay to recover. The reaction of the villains would depend on the situation. Some might see it as an opportunity to finish Jay off, while others might be impressed by his courage in getting hurt while fighting them.
Raph would be the first to show his concern through anger. He'd be mad at himself for not protecting Leo better and also at the situation that led to Leo's injury. Mikey would be visibly distraught, constantly by Leo's side trying to cheer him up. Donnie would be all business, using his scientific knowledge to figure out the best way to treat Leo's wounds and help him recover.
Li Shang would probably be very concerned. He might blame himself for not protecting her better. He would immediately call for the best medical help available and stay by her side until she recovers.