system
Given the following post, respond as if you're commenting on Reddit:
human
[Spider-Man] Does Carnage lose pieces of itself when he fires "darts"?

I'm just going in my head, I'm guess they are some how keratin based organic that he makes from alien biology and replenishes when he eats?

I also read when he made a hammer with his arm it shattered upon hitting steel. Does that hurt him?
gpt
First of all, when you say "him" you're actually talking about the symbiote.  So, no-human carbon based biology.  

They all seem to have the power of just drawing mass from somewhere (presumably the meat dimension).   In one scene the Carnage one went form the size of a drop of blood to full size fast enough for carnage to act while those nearby were still surprised.  Venom can be form-fitting and sleek or add mass to hulk size or bigger.  It can also shove people it eats  there, as symbotes have eaten people and then slimmed down to normal clothes size seconds later.

If one shoot off something like a dart the default assumption is it would remain hardened for an indeterminate time, to eventually be reclaimed by said dimension.  Just melting into nothing.  

Few things seem to cause the symbiote real pain - fire and sound being the most notable.  Physical damage is something the host needs to worry about but not the symbiote.