The main reason why syringes aren’t allowed in games is because of how they’re used in games. Roblox is a kid-friendly platform and they don’t want games to convoy to/encourage children to stick medical needles in themselves or to overdose on drugs thinking they’ll gain superpowers. That’s why you’re prohibited as quoted ‘discussion, depicting, or promoting illegal or highly-regulated activities.’ Reason 2 Die had a problem using pills & painkillers in their game and had to change it where users eat vitamins and cookies instead.
As for your quesiton on blood, you can have blood in your game just as long as it’s not realistic depictions of blood (seems like realistic blood visuals is a big problem emphasised on the terms of service. From my experience the best way to entirely avoid the blood barriers is to avoid using realistic blood pictures/visuals and just go with the classical red blocks/spheres.)
There is however a twist that’s not known to many people and is the fact that if you make your game accessiable on xbox there is a new guideline of rules you have to follow. If does say no blood is allowed but I think that’s just talking about physical blood. So if you have a blood bag, as long as it can’t explode blood out and you can’t see blood inside you should be fine I think.
